The article considers the psychological features and mechanisms of the development of the cognitive sphere of preschool children. The research and conclusions of domestic and foreign scientists on the specifics of the development of various cognitive processes of children are analyzed, summarized and demonstrated. It is concluded that the cognitive processes of a child develop well on the basis of communication with adults, which is an important prerequisite for increasing the initial vocabulary of children. Also, this article analyzes and shows the results of an experimental study on the experimental formation of cognitive processes of preschool children, such as perception, attention, memory, speech, thinking and imagination. It is especially shown that the integration of all cognitive processes plays an important role in the development of the cognitive sphere of the child as a whole.