Motor skills, language, social and personal development as well as cognitive abilities are often the focus of early child development assessment and monitoring. The article presents some of the developmental milestones in these areas of child development. At the same time the article demonstrates that early child development assessment surpasses merely the orientation acording to developmental milestones. As a part of primary health prevention in Slovenia, identification of children with potential developmental delays is performed with the Denver developmental screening test II and the Systematical psychological examination of the three-year-old procedure. The purpose of applying developmental screening tests is early identification of children with developmental problems, as well as preparation of effective early interventions. By applying an appropriate psychological test material, a psychologist is able to assess the type and the stage of child's psychological problems and delays in different developmental domains. Only psychometrically sound, and standardized tests should be applied in the process of early child development assessment. The work presents some of the practical and theoretical difficulties which practitioners are facing in the process of early child development assessment. Some feasible solutions are provided as well.