Low blood glucose is a dangerous violation of homeostasis, especially for infants, children and adolescents, in whom hypoglycemia is often observed, which is explained by immaturity and insufficient efficiency of adaptation reactions, primarily imperfection of hormonal regulators and instability of enzyme systems of glucose metabolism and alternative energy sources, in the form of free fatty acids, ketones, lactate, etc. The special danger of hypoglycemia in children is that glucose, although not single, but a priority source of energy for the nervous structures, therefore the lack of glucose leads to a delay in intellectual development and even to brain damage. At the same time, the lack of stability and clarity of reactions from the central nervous system, somatic and autonomic divisions of the nervous systems characteristic of these age groups, makes it extremely difficult to recognize the hypoglycemic syndrome (HS), and the etiological and pathogenetic diversity of the HS makes its clarifying diagnosis an extremely difficult task. In this regard, the issues of prevention, timely diagnosis, urgent and subsequent therapy of hypoglycemia in newborns, children and adolescents are very relevant. Fulfilled critical analysis of thematic literature over many years, as well as analysis own clinical and research experience. The article discusses the typology of HS from the standpoint of the causes and mechanisms of development, establishes anamnestic and obstetric-gynecological features of the course of pregnancy and childbirth, which predispose to hypoglycemia, clarifies the anthropological and clinical stigmas of HS in the fetus and newborn, which suggests the possibility of hypoglycemia in a child, shows the features clinical manifestations of HS in children of different ages. For clinical practice, an etiological and pathogenetic classification of HS, an algorithm for the treatment of hypoglycemic coma (HC), a scheme for the pathogenetic diagnosis of HS is proposed. Hypoglycemia in infants, children and adolescents is a common syndrome that poses a great danger to the health and development of the child and requires timely and qualified assistance.