Young children infer preferences from a single action, but not if it is constrained.

Inferring others' preferences is socially important and useful. We investigated whether children infer preferences from the minimal information provided by an agent's single action, and whether they avoid inferring preference when the action is constrained. In three experiments, children saw vignettes in which an agent took a worse toy instead of a better one. Experiment 1 shows that this single action influences how young children infer preferences. Children aged three and four were more likely to infer the agent preferred the worse toy when the agent took this toy, compared with when the agent did not take either toy. Experiment 2 then shows that children consider constraints when inferring preferences from a single action. From age 5, children were less likely to avoid inferring a preference for the worse toy when the agent's action was physically constrained. Finally, Experiment 3 provides evidence that children's and adults' sensitivity to constraints, when inferring preferences, is not based on a general notion of constraints, and instead depends on several specific notions. Whereas 5-6-year-olds in this experiment considered physical and socio-moral constraints when inferring preferences, they had difficulty grasping the relevance of epistemic constraints. Adults considered physical and epistemic constraints, but were not influenced by the socio-moral constraint of ownership. Together these findings contribute to a picture of cognitive development in which children are able to infer non-obvious properties on the basis of minimal concrete information, and are also sensitive to subtle changes in this information.