'I'm a big boy, you're a baby': How do such phrases do the vital work of managing young children's peer interactions? We trace the function of such phrases as they were used over an 18-month period by young children (2; 6-4; 11) who attended a New Zealand an early childhood centre. Using interactional sociolinguistics methods of analysis we examine how children used particular phrases within their community of practice to manage their peer interactions and to mark out individual and group identities through inclusion and exclusion. The phrases we analyse are labels (big boys; baby); we document changes in the way they were used productively: there is 'ownership' of them; then they are re-purposed; and then some disappear. By viewing peer interactions as phenomena that include a temporal dimension, we trace how each phrase helped to establish individual and group identities that were constantly open to negotiation. We argue the need for greater attention to children's use of language to improve our understanding of children's lived experiences of peer interactions including inclusion and exclusion processes in early childhood settings.