A method for eliciting extended explanations was used to evaluate predictions from the "theory-theory" account of developing psychological reasoning. Children were repeatedly asked to explain the actions or emotions of story characters with false beliefs. Questioning elicited false belief attributions in half of 3-year-olds (Study 1, N = 16, age M = 3;6) and most 4-year-olds who failed belief prediction tasks (Study 2, N = 30, M = 4;5). In Study 3, 30 prediction failers (M = 5;1) gave significantly more false belief explanations for emotions than for actions. Across the studies, desire and emotion explanations emerged early and often, reflecting the primacy of these constructs in the children's understanding of psychological causality. Results are discussed in terms of their implications for developmental mechanism. (Contains 3 tables.)