Recent experimental evidence suggests that adults incorporate speaker knowledge into the derivation of pragmatic implicatures. Developmental studies report that 5-year-old children also succeed in taking into account speaker knowledge in implicature computation, but 4-year-olds fail. The present study investigated the pragmatic competence of 4-year-olds, specifically the ability to incorporate speaker knowledge into the derivation of ad hoc scalar implicatures. Using a simple paradigm inspired by referential communication, we found that 4- year-olds are able to incorporate speaker knowledge into implicature derivation. These results have implications for our understanding of the linguistic, pragmatic, and epistemic abilities of young children.