A large body of work has focused on children's ability to attribute mental states to other people, and whether these abilities are influenced by the extent and nature of children's social interactions. However, it remains largely unknown which developmental factors shape children's ability to influence the mental states of others. Building on the suggestion that collaborative experiences early in life might be crucial for the emergence of mental coordination abilities, here we assess the relative contribution of social exposure to familial and non-familial agents on children's communicative adjustments to their mental model of an addressee ('audience design'). During an online interactive game, five-year-olds spontaneously organized their non-verbal communicative behaviors according to their beliefs about an interlocutor. The magnitude of these communicative adjustments was predicted by the time spent at daycare, from birth until four years of age, over and above effects of familial social environment. These results suggest that the degree of non-familial social interaction early in life modulates the influence that children's beliefs have on their referential communicative behavior.