The paper describes an experimental study of relations between children in mixed-age kindergarten groups in comparison with groups of children of the same age. Observation and comparative experiments have demonstrated wide variability of relations between children in mixed-age groups: from support and cooperation to suppression and humiliation of younger children by older ones. At the same time each mixed-age group was characterized by a single dominant pattern of relations. Alternatively, in homogeneous age groups varying patterns of interpersonal relations can be observed. The study proves that the principal factor determining relations between children is the teacher's communicating style: senior children reproduce that style in their interaction with younger children. The paper also analyzes different pedagogical styles and their influence on the character of interpersonal relations in a mixed-age group.