We explore the developmental trajectory and underlying mechanisms of relational reasoning. We describe a surprising developmental pattern: Younger learners are better than older ones at inferring abstract relations. Walker and Gopnik (2014) demonstrated that toddlers are able to infer the relations “same” and “different” in a causal system. However, these findings appear to contrast with the literature suggesting that older children have difficulty inferring these relations. Here we manipulate the data and children’s search procedure to assess the influence of these factors. In Experiment 1, we find that while younger children have no difficulty learning these relational concepts, older children fail to draw this abstract inference. In Experiment 2, we demonstrate that older children have learned the hypothesis that individual kinds of objects lead to effects. Finally, Experiment 3 indicates that including an explanation prompt during learning also improves performance. Findings are discussed in light of computational theories of learning.