Introduction. The article is devoted to the problem of complex study of early development of children with down syndrome based on the principles of ICF. The analysis of the comparability of parameters describing the current level of development of a child with normal and impaired ontogenesis in popular methods of early development diagnostics with the description parameters adopted in the new classification system of the ICF Presents the experience of processing and interpreting the results of psychological and pedagogical study of the cognitive, speech and motor spheres of young children in the context of the severity of restrictions on their daily life and health. The article describes the method of establishing a functional and rehabilitation diagnosis, as well as the procedure for documenting the results of the psychological and pedagogical study, taking into account the classification categories adopted in the ICF. The significance of the results obtained for the interaction of an interdisciplinary team of specialists within the framework of the early aid Service is determined.Materials and Methods. When writing the article, we used methods of studying domestic and foreign literature sources; generalization and systematization of the results of studying the cognitive, speech and motor spheres of young children with down syndrome; experimental methods and scales for assessing the timeliness of early childhood development.Results. The variety of approaches to studying the development of children with normal and impaired development in early ontogenesis is considered. Based on the study of domestic and foreign literature sources, the most common methods of comprehensive assessment of the cognitive, speech and motor spheres of young children with developmental disabilities were selected and their comparability with the description parameters adopted in the ICF domain classification system was evaluated. Data analysis has shown that in the process of studying individual or systemic indicators of early development of young children with down syndrome, any diagnostic tools familiar to the specialist that have passed the procedure of experimental testing and validation can be used. At the same time, only the process of processing, interpreting and finalizing the test results in the Protocol needs modification, while the stimulus material and the research procedure do not need any modification.Discussion and Conclusions. The study concluded that the ICF can be effectively applied at all stages of the study of young children with not only down syndrome, but also any variants of impaired development. The introduction of ICF profiles in the process of documenting the results of primary diagnostics and dynamic monitoring ensures consistency of interaction between specialists of the early care Service both within the organization and at the interdepartmental level