This longitudinal study examined the social interactions of children with mild developmental (cognitive) delays with friends across the early childhood and early elementary years. Results revealed increases in many forms of social exchange with effect sizes in the moderate range, but no changes in sustained interactive play. Social interaction patterns, difficulties in identifying friends to participate in the study, and concerns evident in children's peer and friendship networks suggest the general absence of reciprocal friendships. These findings are consistent with the hypothesis that children's limited peer-related social competence constrains all aspects of their development of friendships. Despite these problems, the potential benefits of interventions designed to support relationships at this stage of friendship development for children with delays were noted.