The present studies investigated 3-year-olds’ ability to adapt their communication based on their parents’ knowledge state when requesting familiar and novel objects. Children participated in a toy retrieval game during which their parent was present or absent during toy introductions. In Study 1, children used more specific requests and cue combinations in the parent-absent group versus parent- present group when requesting familiar labelled objects. In Study 2, a similar game was administered with adaptations to reduce cognitive demands. Children produced more specific requests in the parent-absent group compared with the parent-present group when requesting an unlabelled novel object. The results indicate that three-year-olds have an emergent ability to adapt their communicative behaviours based on their parents’ knowledge state.