Age‐related changes in flexibility and automaticity of reasoning about social situations were investigated. Children (N = 101; age range = 7;8–17;7) were presented with the flexibility and automaticity of social cognition (FASC), a new measure of social cognition in which cartoon vignettes of social situations are presented and participants explain what is happening and why. Scenarios vary on whether the scenario is socially ambiguous and whether or not language is used. Flexibility is determined by the number of unique, plausible explanations, and automaticity is indicated by speed of response. Overall, both flexibility and automaticity increased significantly with age. Language and social ambiguity influenced performance. Future work should investigate differences in FASC in older populations and clinical groups.