A person who changes their mind signals that they have encountered new information that prompted their belief shift. Can children use their developing understanding of third-party belief revision to take advantage of this signal for their own learning? Children (5;0-9;11 years) played a Whodunit-style game in which detectives updated their beliefs in response to different clues. The clues in isolation were meaningless to participants. In simple cases, children accurately inferred the meaning of the clues based on how they changed others’ beliefs. With age, children more readily integrated changes in agents’ certainty to guide these inferences. These findings suggest that children can draw reverse inferences about evidence by leveraging a causal understanding of how it impacts an agent’s beliefs. Thus, children may learn world knowledge indirectly by observing its effects on others’ minds.