Human beings infer complex mental states given very little information—a facial expression, a sarcastic tone, or even a simple behavior. Previous work suggests that adults make joint belief and desire inferences based on an actor’s path, and that these inferences are well-explained by a Bayesian framework (Baker, Saxe, & Tenenbaum, 2011). We investigate the development of this ability by assessing mental state inferences made by children ages 3-6 after watching a short movie. Our results suggest that young children spontaneously make inductive inferences about desires or preferences, and that the ability to infer belief from behavior develops between ages 3-6, and possibly throughout later childhood. We formulate three computational models that capture the developmental shift between non-representational and representational theory of mind, and show that these models capture qualitative patterns in the children’s data.