To help children navigate their social environments, adults must understand what children know about race, and when they acquire this knowledge. Across three preregistered studies, we tested United States adults' knowledge of when children first use race to categorize and ascribe traits to others. Participants wildly-and uniquely-misjudged children's abilities to process race. This inaccuracy was consequential: it was a stronger predictor of the preference to delay conversations about race with children than other factors previously theorized to underlie adults' reluctance to talk about race. And, this relation was causal. Our data suggest that fundamental misunderstandings about children's capacities to process race are pervasive in the United States population and may delay when adults engage children in important conversations about race. (PsycInfo Database Record (c) 2021 APA, all rights reserved).