The theoretical analysis of modern research on the phenomenon of psychological well-being allows us to identify the essence and features of child's psychological well-being. It is shown that there are different approaches to its evaluation (analysis of individual determinants of well-being and contextual analysis), which reflect the evolution of approaches to studying the phenomenon of happiness and human well-being in historical and scientific contexts. An analysis of Ukrainian and foreign studies shows that psychological health is most often singled out as the main component of psychological well-being. There is a difference between the concepts of psychological health and mental one. In the legislative documents of Ukraine, these definitions began to be used more often as the purpose of the activities of institutions related to the child. There is a difference between ways of assessing the psychological well-being of preschool, primary school and adolescent children. Parents' assessments of young children are often irrelevant and cannot be an indicator of their child's psychological well-being. Alternatively, it is suggested to study the relationship of parents with the child as a factor of its well-being. Positive psychology had a great influence on the study of the child's psychological well-being, and the idea of the child's positive development as a result of constructive socialization and the process of individualization can become a reference point in building a child's well-being environment. It is proved that the analysis of the environment (theory of ecosystems) of the psychological well-being of the child is one of the promising areas of research and a popular applied practice. Foreign programs for the development of emotional and psychological well-being in schools are analyzed: SEL, Zippy's Friends, MindMatters, The Olweus Bullying Prevention Program (OBPP).