The article examines the system of views of the Russian writer L.N. Tolstoy (1828-1910) about mental development at the first stage of childhood in the story of the same name (1852). The deep emotional and personal connections of a child with his mother turn this time of life into a happy, unforgettable time, satisfying his need for the boundless love of the closest person. A holistic picture of mental development represents, on the one hand, the interconnections of its factors - the social world of the noble family and secular society; close direct communication with close adults and children; the child’s mastery of various types of activities provided for by the home education of the nobility; cognitive activity of the child aimed at entering society and understanding it. This picture, on the other hand, reveals the comprehensive formation, integration of all spheres of the child’s mental life - feelings, mind, actions in the uniqueness of worldview, self-awareness and introspection, the search for moral criteria for distinguishing between good and evil, the child’s individuality, which develops as the degree of expression of certain features in all areas of development. The main acquisitions of mental development are awareness, arbitrariness of behavior, activity, feelings, the ability to manage them and control their course. The happy era of childhood ends with the child’s meeting with the tragic secret of human existence - the death of a loved one, the resulting experience of irreparable loss, the severance of irreparable emotional and personal ties with the closest, dearly loved adults and home, marking the transition to a new era - adolescence, where there is grief and suffering, separation and sadness.