This research examines how language (generic vs. specific) and speaker knowledge (knowledgeable vs. unknowledgeable) influence essentialist beliefs about a novel social category in children and adults. Across two studies (N = 448 children, 433 adults), adults were more likely to endorse essentialist beliefs when knowledgeable speakers used generic descriptions. Children’s responses varied by evaluation timing. In Study 1, when test questions were delayed, children’s essentialist beliefs were influenced by language but not speaker knowledge. In Study 2, when memory demands were reduced by having children evaluate claims immediately after hearing them, children showed sensitivity to speaker knowledge, mirroring adults’ responses. These findings highlight the role of language and contextual cues in shaping essentialist thought about social groups, suggesting that the effects of generics on social thought are dependent on the cultural expertise of the speaker.