The significance of studying the prevalence, age- and sex-related differences and diagnostic aspects of schizophrenia spectrum disorders (F2 Schizophrenia, schizotypal and delusional disorders) in pediatric and adolescent patients of mental health facilities is linked to the upcoming release of the International Classification of Diseases, Revision 11 (ICD-11). Its whole chapters have been updated, including disorders in the schizophrenia group. Diagnostic challenges posed by this debilitating group of mental disorders are associated with the diversity of clinical presentations, the incompleteness of psychopathological phenomena syndromes, and vague atypical symptoms. Changes in the prevalence of these disorders identified by the analysis of medical records at a mental health facility for children (a decline in the number of patients with F20, schizophrenia, and a surge in the number of patients with F21, schizotypal disorder) and significant disagreement about and disagreement about the diagnostic criteria for schizophrenia spectrum disorders in children and adolescents, evaluation of their dynamics, outcomes, and the social functioning of the patient necessitate further prospective follow-up studies aimed at overcoming the identified difficulties in the diagnosis, treatment and rehabilitation of such patients.