What events trigger causal explanatory reasoning in young children? Children's explanations could be triggered by either consistent events (suggesting that explanations serve a confirmatory function) or inconsistent events (suggesting that they promote discovery of new information). In 2 studies with preschool children (N = 80), events that were consistent with children's prior knowledge were simultaneously contrasted with events that were inconsistent with prior knowledge, and children were invited to explain either outcome (or both). Results demonstrate that inconsistent outcomes are an especially powerful trigger for children's explanations and that the explanations children provide for inconsistent outcomes refer to internal causal properties, overriding perceptual appearances. In sum, the data provide empirical evidence that inconsistent events motivate children to construct explanations, thereby suggesting that children's explanations function in the service of discovery.