Early Childhood Development (0 - 6 Years Old) from Healthy to Pathologic: A Review of the Literature

Early childhood development involves an appropriate global intervention concerning the different areas of development such as: physical, cognitive, language and socio-emotional [1]. Especially during the first six years of life in an adequate environment rich in exchange and interaction. We will present in this article a review of the literature concerning normal early childhood development, focus firstly in normal development’s steps, the importance of first experiences and first aid with a stable and caring attachment figure. second, we will describe the various developmental disorders, occurring during this age group which extends from birth to 6 years and based on the DSM5 classification, namely that developmental delay may concern only one aspect of development (e.g. language delay or motor delay specifically) or concern the different aspects of development (overall development delay). The dynamics of development is also important to clarify because schematically we contrast the pathologies fixed to progressive pathologies (where we find the concepts of stagnation or regression in the development of the child). We will discuss in the third chapter, the interest of early detection as well as the multiple clinical and psychometric diagnostic tools, which aim to detect any delay or disorder in order to initiate appropriate care and minimize the long-term


Introduction
The development of the child implies a dynamic, an evolution, and all of the successive processes which, in a determined order, lead an organism to maturity [2]. This continuous process follows the same sequence in all children and is closely linked to the maturation of the nervous system. Also, it is considered to be the result of various environmental internal genetic forces, epigenetic depending both on the characteristics that the child has at birth (innate) and on the contribution of acquired experiences.
Each year, more than 200 million children under the age of five fail to reach their full development potential due to their exposure to multiple problems, including poverty, malnutrition, poor health and an unstimulating family environment, which slow down their physical, cognitive, language and socio-emotional development [1] [3] [4]. Open Journal of Medical Psychology WHO [13], the mother must be in good physical and emotional health before and during pregnancy for the foetus to develop optimally. By definition "Optimal development of the fetus" is his state at birth which offers the newborn the greatest chance of surviving and thriving during the neonatal period and early childhood and which predisposes it so that its initial development does not have no harmful consequences later in its existence.

Prenatal Period
From conception to birth, the child already has a singularity and a history. This prenatal period is characterized by 2 processes: The rapid growth of the fetus and the maturation of organs and tissues and its development which essentially depends, during the first trimester, the initial phase of gestation, on genetic factors.
At the end of the first trimester, all the organs are formed and functional, the fetus gets to know him and his universe and will acquire sensitive and sensory skills allowing him to perceive, act and interact in his environment while keeping in mind the intrauterine experiences. Later, during the second third trimester, the factors linked to the environment and to the hormonal state become preponderant.
The brain during fetal life is still in full development. The underlying mechanisms are multiple (neurogenic, gliogenic, migration, neuronal differentiation and apoptosis, synaptic, dendritic and axonal growth, proliferation and elimination; myelination of white matter fibers ...) and the brain changes are particularly intense during the last weeks of pregnancy and the first postnatal months. This stage is particularly vulnerable to any disturbance of the biological and nutritional balance [14].

Postnatal Period
1) The theory of Piaget (1896Piaget ( -1980 Piaget, one of the first founders of developmental psychology, proposed 4 stages of cognitive development in children: Sensorimotor stage (0 -2 years) (Permanence of the object, mental representation, delayed imitation), the stage preoperative (2 -7 years) (Language, drawing, intuitive reasoning), concrete operating stage: classification and serialization (7 -11 -12 years) and formal operating stage: reasoning (12 years -adult). However, the study will focus mainly on the first two stages: sensorimotor stage and the preoperative stage.
The sensorimotor period (0 to 2 years): During this phase, the baby mainly uses his senses and his motor skills to explore and adapt to his environment. The role of the environment, and in particular of the parents, is therefore crucial, according to Donald Woods Winnicott "A child alone without his environment, it does not exist", it is essentially the mother-baby couple based on the interactions between needs and responses. Bowlby in his writings says that even feeding a child is not enough to ensure emotional security, continuous relationships with Open Journal of Medical Psychology stable figures are important for a child's psychological development. The child is therefore an active agent in interactions with his environment and the emotional bond woven with the parents now becomes the main determinant of the quality of development [15]. The infant is thus both stimulated and reassured. It is the quality of the interaction with the environment that will, in large part, determine the future possibilities for the expression of these skills.
Winnicott also mentions a period which extends from 0 to 5 months, corresponding to "the primitive psychic phase", during which the child must be fed, cleaned and where the role of the caregiver is crucial. This is the "primary maternal concern" a state of empathy of the mother who identifies more or less consciously with her newborn to know what he needs, how to carry it ("holding") and how to treat it ("handling") [16].
At the age of 9 months, the baby is sitting without support, able to pick up toys, transfer them from hand to hand and able to pick up very small objects between the thumb and the first finger, babbling consonants and vowels and modulates the height and volume. He is able to understand his needs for eating, drinking and the need for diaper changes. This period was dominated by considerable progress in sensorimotor action or "sensorimotor intelligence" without thought or representation. According to Piaget, this is the stage of the permanence of the object, mental representation, delayed imitation. Language, admittedly limited in space and time, is based on action and perception. The child is in a state of initial indifferentiation with the environment, but he will gradually build the notion of object, during various adaptive interactions between the reflexes that the child has at birth and the situations of the environment to which he will be confronted.
Infant-juvenile period: 2 to 6 years: This is the stage of access to Representative Intelligence: to attribute a kind of mental presence to an absent object. The differentiation of a signifier and a signified. The child then becomes capable of representing an absent signified (representation of the object) by means of a present signifier (the word, symbolic play, drawing) and by using signs and symbols = semiotization. Passage also from sensorimotor schemas to conceptual schemas which manifests itself in the simultaneous appearance of deferred imitation behaviors, symbolic games, drawing, mental images (internalized imitation) with an explosion of language around the age of 3 years. The child thus gains in independence and insurance.
At the age of 4, the neurological system becomes quite complex. The child can ask more complex questions: when, why and how, understands the feelings of others, better accepts the limits imposed by adults, manages frustration and opposites better, and is able to follow a set of instructions more complex thereafter.
2) The epigenetic theory of Wallon It is a concrete multidimensional approach. According to Walloon, the child is already a social being and actively participates in its development, his theory offers 6 stages: food function becomes more complex. The child will then experience the sufferings of waiting or deprivation, which are manifested externally by spasms, tenses and cries [17]. • The emotional stage (from 2 to 3 months up to 8 -12 months): this stage peaks around the middle of the first year. During this stage and around 3 months the child already knows how to send to those around him, and particularly to his mother, smiles and signs of contentment which are already an emotional bond. At the level of the mother-child relationship, it is a transition from a simply physiological symbiosis to an emotional symbiosis.
Throughout this stage, multiply and refine exploratory reactions which prepare the next stage. year, the child enters the projective stage: it is the establishment of a representative intelligence which takes its source in the game of attitudes and it requires the use of language to refine fully [17].
• The stage of personalism (between 3 and 6 years old): in this stage the self-arises by opposing (personality crisis) and an attitude of refusal becomes usual as if the only concern of the child was to safeguard the newly discovered autonomy of his person. The perception of the presence of others gives rise to inhibition reactions, to manifestations of shyness accompanied by clumsiness. Towards 5 -6 years especially, the personalism of the child results in a new form of differentiated relations with others; this is the rise of an imitation of a model (favorite character and often jealous). Self-care also involves an essential reference to others and the child can only please him if he feels he can please others. Thus personable reactions invade the child's behavior and the aggressive or arrogant tone becomes conciliatory or seductive.
And the last two categorial stages (6 -11 years) where there is intellectual predominance, differentiation between objective and subjective and the stage of puberty where the demands of personality come to the fore. Walloon therefore has a more general approach, more global than that of Piaget, because he was interested in the construction of the personality encompassing social, intellectual and emotional dimensions as affectivity or intelligence.

Domains of Development
Early childhood development takes place in several interrelated areas: physical, cognitive, language and socio-emotional. Each of these areas influences and depends on the others. To distinguish, during this development, two different but complementary phenomena: physiological growth which is defined as a change in size and weight gain and psychological development which is characterized by the evolution of skills and functions. One organ in particular plays an essential role: the brain.

Brain Development
Brain growth is the consequence of the increase in the volume occupied by cells (neurogenesis and myelination), and the functional maturation of cells and their connections (synaptogenesis). One of the characteristics of the cerebral architecture of the child's brain compared to the adult brain, is the notion of neuronal and synaptic redundancy. It is important to recognize that the nervous system continues to reshape and change not only in early development, but throughout life in response to environmental influences as well as genetically programmed events [18]. The majority of brain growth takes place in the first year and the vast majority before 4 years. At birth, the brain has already reached 25% of its adult mass, 66% at 1 year and 90% at 3 years [19]. Thus the relationships and bonds that we weave from birth through interactions, experiences, stimuli, influence the development of nerve connections.
The priority role of parent-child interactions should be emphasized, with parents being the primary stimulants in early childhood.

Postural, Sensory and Motor Development
All the senses are very developed from birth except that of sight, but very quickly the vision of the child improves day by day. Motor skills are dependent on two systems: The lower or cortico-spinal system whose maturation is early and ascending and is expressed during the third trimester of pregnancy and, the upper or cortico-spinal system which begins at birth and whose maturation is later and descending.
Indeed, examination of the newborn reveals the presence of so-called archaic or primary motor reflexes, spontaneous movements with hypertonia of the limbs and axial hypotonia. The development takes place according to a cephalo-caudal progression and, is marked by the progressive disappearance of reflex motor skills around the age of 4 months, the relaxation of the passive tone of the limbs and the progressive installation of a controlled motor skills more and more precise and quick between 5 months and 5 years. These motor acquisitions have an important functional and adaptive value and are the sign of a good maturation and a good functioning of the upper cortico-spinal system [20] [21]. Motor acquisitions are dependent more to brain maturation, perceptual and cognitive capacities and also experience [22]. The first is little influenced by intelligence Open Journal of Medical Psychology and the environment and the acquisition sequences are little affected by specific sensory impairments (blindness, deafness). Fine motor skills, which essentially concern handling skills, are dependent, in addition to brain maturation, on the child's visual and cognitive perceptual capacities.

Cognitive Development
The word cognition comes from the Latin "cognocere" (to know). Cognition is defined as the set of processes that allow the processing of information and the constitution of knowledge. Cognitive development (of knowledge), refers to thinking, reasoning and intelligence. Cognition (or thinking) has several broad categories: perception, memory, learning, language, intelligence, reasoning, attention processes and decision making. The child acquires knowledge during the 0 to 5 year periods. Encouraged and stimulated by those around him, the child gradually explores, discovers, experiments and builds knowledge of his environment.
The first to propose a model of intellectual development for children is Piaget

Psychoaffective Development
Psycho-emotional development refers to the bonds that the child establishes with his parents and to the expression of his feelings and emotions which he learns to manage little by little.
This area of development is very important based on the parent-child relationship. By the signals, the responses, the reactions on the part of the child and the parents, there is established an "interactive synchrony" and a reciprocity in the relationship. Parents have a primary role in establishing the bonding relationship through their attitude, behaviors and how they respond [23]. This reciprocal affective relationship which is gradually built up between the child and the stable figures, will have an important influence on personal security, confidence, autonomy, socialization, in short on the development of the personality of the child.

Social Development
As the family is the first place of socialization, the parents will influence the development of the child's social skills. They can, for example, teach him strategies to get in touch with others, to develop empathy, etc. The relationship developed

Development or Neuro-Developmental Disorders
"Developmental disorders" means any situation of maladjustment, any difficulty or problem which has the characteristic of presenting disturbances in the acquisition, assimilation or application of specific skills or sets of information. Those disorders generally appear during early childhood and are characterized by developmental delay, result in cognitive, behavioral and sensorimotor impairments leading, among other things, to dysfunction of attention, memory, perception, language, problem solving or social interaction. However, it often takes several years between the appearance of the first symptoms and their detection.
Developmental delay may relate to a single aspect of development (language delay or isolated motor delay, etc.) or in different aspects of development (overall developmental delay) [27].
Currently, the AAP [28] specifies that Developmental delay: if and only if the functional skills do not appear at the expected age, but the usual sequence of appearance is respected. The delay can be global or dissociated. Developmental disorder: is identifiable when an abnormality of the neurological or developmental examination is associated with a functional limitation, in this case, the acquisitions are not delayed, but deviant, not resembling the usual sequence of maturation of a function [29].
Several epidemiological studies [30] [31] show that approximately 10% to 15% of children between 3 and 5 years old, present problems in behavior or in the sphere of effects, 50% of them they will continue to present these problems dur-  [33].
Longitudinal studies [34] also make a link between early behavioral and emotional difficulties and adult psychopathology. These studies allow us to conclude that the quality of parent/child interactions is strongly associated with the severity and continuity of behavioral problems in young children.
Lavigne [31] note that dysfunctional or "inconsistent" parent/child interactions and a disadvantaged family and social environment are associated with maintaining behavioral difficulties between the ages of 2 and 5 years, the study by Ana Sancho Rossignol in 2005, shows the existence of links between dysfunctions in early parent/child interactions, behavioral problems and the presence of "preforms" of psychopathological organization in very young children [35].
The model of psychopathology thus goes from a direct dyadic and causal mode, where psychopathology is the consequence of disorders of the motherchild relationship, to a sequential and systemic, family model, proceeding in stages, depending on the intensity risk and resilience factors, and on a model of genetic susceptibility influenced by the environment [36].
One in 150 newborns are affected by an autism spectrum disorder; 1 to 2% of the population has an intellectual disability, the leading cause of disability in children; 5% to 10% of children, all "DYS" disorders combined, including 5% by written language disorders, presence of comorbidity in almost 40%, (several types of disorder), among children with one or more "DYS": 1% have a severe form; 2% to 5%: HPI (high intellectual potential) recognized as a disability according to the minimum intellectual quotient threshold used; 10% to 15% of children with simple learning delay, the causes of which can take root in the child's environment.
The cause of developmental delays is not always identified despite a detailed etiological assessment in 40% to 50% of cases. The dynamics of development are important to clarify because schematically we contrast the pathologies fixed to progressive pathologies (where we find the concepts of stagnation or regression in the development of the child).
In the face of any concern in this area, instead of just waiting and seeing, it is recommended to use standardized screening tools. These disorders can be mild and easy to manage with educational and behavioral interventions, or they can be more severe and children affected by them are likely to require more assistance.

Classification of Disorders
Early childhood development disorders from 0 to 6 years old can be classified according to whether they are more related to: The influence of the environment

Description of the Different Early Childhood Development According to DSM5
Developmental disorders include cerebral palsy, developmental delay, mental handicap, primary language disorder or dysphasia, autism spectrum disorder (ASD), attention deficit disorder with/without and hyperactivity (ADD/ADHD), learning disabilities, coordination acquisition disorder (CAD) as well as genetic and chromosomal abnormalities.  Often "on the breach" or "mounted on springs"; Talks too much; Rushes to answer questions; Difficulty waiting his turn; Interrupts others or imposes himself).

Neuro-Developmental Disorders
These inattentiveness or hyperactivity-impulsivity symptoms were present before the age of 12, and they are present in two different contexts (eg school and home). In addition, Autism Spectrum Disorders are no longer considered to be incompatible with a diagnosis of ADHD.

Other Development Disorders
Oppositional Provocation Disorder: Angered/irritable mood, quarrelsome/provocative behavior, or a vindictive spirit persisting for at least 6 months during which at least 4 (or more) symptoms of the following categories are present, and manifesting itself during interactions with at least one subject external to the siblings. Sleep-wake alternation disorders: These disorders involve a disturbance in the quality, schedule or duration of sleep, a disturbance which results in an alteration in daytime functioning and causes mental distress. In all cases, you must first specify whether the disorder is Episodic (lasting at least one month but less than three months) or Persistent (lasting more than three months), or Recurrent (at least two episodes in one year), then if it is Acute (having lasted less than a month), Subacute (having lasted more than one month and less than three months) or Persistent, (having lasted more than three months) and finally if its level of severity is Mild (difficulty in maintaining daytime alertness one or two days a week) Medium (difficulty in maintaining daytime alertness 3 to 4 days a week) or Severe (difficulty in maintaining daytime alertness 5 to 7 days a week). Neurocognitive Disorders: These disorders are characterized by changes in the structure of the brain and its functioning, which results in impaired learning, orientation, judgment, memory and intellectual functions. These disorders were formerly called dementia, delirium, amnesic disorder and other cognitive disorders.

Support of Early Childhood Development Disorders (ECDD)
Identifying difficulties early allows you to intervene without delay and to be more effective. Interventions via the ECDD, must target the many risks that children undergo early. These are reactive disorders, which are not yet registered in the child's psyche and which have not yet given rise to harmful relationship vicious circles. These situations most often, but not always, show great plasticity and a potential for reversibility at a time when the development of the brain is in its most intense phase "The plasticity of the brain compensates for certain deficiencies". And if the disorders are more serious, it is important to treat them early in life to prevent the child's development from being too much affected [41]. The earlier we intervene, in a favorable and sustained manner, the better the results. This is more effective than trying to remedy cumulative deficits later in life [42]. When the disorder results from a trauma, the intervention will be mainly environmental and will focus on the practical consequences of the trauma.
In the case of an affective disorder, therapeutic interventions must above all focus on the quality of the parent/child relationship. On the other hand, when it is a regulatory disorder or a relationship and communication disorder, the interventions should be primarily educational in nature and relate, for example, to sensory integration or the child's motor skills. In all cases, the objective will be an early detection of the delay to initiate appropriate care and minimize the long-term consequences.

Development Screening and Diagnostic Tools
To identify people with ECDD, a comprehensive assessment should include historical information such as a pregnancy, labor, delivery, first neonatal treatment, history of development, and communication milestones and motor skills.
The medical history should include screening for sensory deficits (hearing or visual impairments, for example), as well as a discussion of other medical conditions and specific signs and symptoms. History and physical examination may assist in the search for known or associated etiological conditions.
The delay will be confirmed by the use of calibrated tests, the passing of which will be carried out by the appropriate professional (e.g. passing of a psychometric test by a psychologist or neuropsychologist, taking of motor tests by a psychomotrician, passing of language tests by a speech therapist).
However, screening requires neuropsychological evaluation by qualified health professionals experienced in the use of the guidelines using age-appropriate tools and scales involved in the diagnosis of the disorder early childhood development (ECDD) to confirm or not the diagnosis such as for: IDI (Infant Development Inventory): The Infant Development Inventory [44] was developed by Ireton to cover the period from birth to 21 months of age.
Parents describe their infant in terms of current behaviors using an Infant Development Chart, describing patterns of behavior expected across the five domains of fine motor, gross motor, social, self-help and language. The IDI is a descriptive tool which health professionals ask concerned caregivers to complete at-risk infants are referred for subsequent assessment. Ability to follow the adult's score [47], and other test for Autism spectrum disorder as: ADOS, ADI-R, CARS.
ASQ: SE (Ages and Stages Questionnaire: Social-Emotional). The ASQ: SE is a brief parent-or teacher-reported instrument designed to assist in identifying developmental delays in children aged six to 60 months. There are three response options (rarely or never, sometimes, most of the time) for each item, which are scored zero, five, and ten with a possible additional five points if this specific behavior worries the informant. A total difficulty score is calculated by adding the points from all the items and the items related to expressed concerns [48].

Remediation
According to the National Institute of Child Health and Human Development, there is currently no single, definitive treatment for ECDD remediation. People with ECDD have a wide range of behaviors and abilities, so that no approach is as effective for everyone, and not everyone involved in outcome studies has benefited to the same extent.
In addition, people with ECDD may need new and/or multiple sets of care or changes in the frequency and duration of existing services. These changes are usually based on a review due to the severity of the current situation, as well as changes related to growth and development, caregivers, the environment, or functional requirements. We know that remedial actions will be all the more effective in preventing school failure because they will have been implemented as early as possible, during the most favorable period of development.
The main objectives in the management of TDPE are to minimize the main characteristics and associated deficits, to maximize functional independence and quality of life and to relieve family distress [52], but also to include services such as, but not limited to:  researches in different neuropsychologist scales), allows the caregiver to focus on the parents and to focus on the baby and its primitive experiences. This can serve as a medium and allow some parents, who are more suspicious or in denial, to feel less threatened, to relax and to give themselves up a little more.

Conclusions
Early childhood is of crucial importance in relation to child development. Several research results reported in the literature indicate considerable changes at all levels of child development. These changes are constantly subject to various sources of influence, coming from his environment or inherent in himself and his type of evolution and therefore, subject to change. However, in order to guarantee good development for each child, early identification and treatment must be established. Several situations can be modified in this way and others are treated and resolved, others are also dealt with so that the harmful consequences are minimized and the child arrives at the best possible development.

C. Meriem et al. Open Journal of Medical Psychology
As a result, screening, diagnosis, care and support for the child are based on good interaction between care providers, making sure to give families a special place throughout the process and, ensuring a suitable orientation taking into account the economic and geographic reality of families. Several research studies show that high quality integrated programs are needed globally to ensure that all children reach their full potential and thrive.