Throughout the world, societies discriminate against and mistreat members of certain social groups. Young children may express intergroup biases that lead to such outcomes, demonstrating preferences for their own over other groups. How these biases develop is an important topic of study in today’s climate. A new longitudinal study mimicked a situation in which children might overhear derogatory messages about a new social group. The study revealed that overhearing a stranger’s negative claims about a social group, even in a brief comment, can have a lasting influence on children’s attitudes towards the group.