This article explores the ways that mothers and children from primarily middle-income European American backgrounds reason about events in which biological and nonbiological objects change in size. In Study 1, mother–child conversations were examined to investigate the events mothers described as growth, as well as the ways mothers explained events occurring in different domains. Findings indicate that although mothers primarily discussed events in domain-specific ways, they exhibited some domain blurring in their talk to children. In Study 2, 3-year-old children (M=3 years, 2 months) and 5