The article justifies the need for early diagnosis of mental and physical developmental disorders in young children. The article describes the basic principles, approaches, and features of the psychological and pedagogical diagnosis of the development deviations in infants and young children. Recommendations for the tools and methods of the diagnosis of young children are given, based on the need to assess certain skills and functions. The main factors that influence the mental and physical state of young children are characterized. The article gives recommendations for the duration of the diagnostic procedure and basic requirements for the premises for conducting a psychological and pedagogical diagnosis of the development of children. The main methods and techniques, used in the diagnosis of young children, are presented. The authors of the article identify the problem of negative impacts of the social environment on the formation of a complex system of sensory receptor connections and the mental state of a child. The article describes the influence of the birth of a child with developmental disabilities on the family and the features of the emotional response to the diagnosis or medical report. The objectives and the characteristics of counseling parents of children with disabilities are given along with the content of the initial stages of counseling and support. The relevance of using online counseling for parents is also identified. The article describes the organizational model of work with the “child-parent” system and characterizes the main pedagogical conditions, which are the most favorable for the development of a child.