A field investigation of 32 groups of communally reared children utilizing 10 categories of group behavior reported group behavior forms and child socialization in groups of toddlers and preschoolers 18 months to 42 months of age. The groups were equally divided (16 each) among "total" and "day care" types and were age-homogeneous. Group forms were grouping, monitoring, imitation, affective responses to others, object transactions, helping, norm behaviors, importance establishing, organizing and boundary behaviors. Monitoring, grouping, organizing and norming showed direct age changes but degree and kind of contact influenced grouping as well as imitation and object transaction. Helping, boundary behaviors, affective responses and establishing importance were infrequent in our observations. Some group interactions were found to be more facilitative of socialization at earlier ages than is generally thought likely. It is suggested that group forms could be employed as socialization criteria for social development and as diagnostic aids. Further study should chart one or two group forms over a greater developmental span. (Author)