We investigate young children's capacity for “causal relational reasoning”: the ability to use relational reasoning to design novel interventions and bring about novel outcomes. In two experiments, we show that 24–30-month-old toddlers and three-year-old preschoolers use relational reasoning in a causal problem-solving task. Even toddlers rapidly inferred relational causal rules and applied this knowledge to solve novel problems––thus demonstrating both surprisingly early competence in relational reasoning and sophisticated causal inference. In both experiments, children observed a handful of trials in which a mechanistically opaque machine made objects larger or smaller. When prompted to solve a new problem, they used the machine to change the relative size of a novel object – even though its appearance and absolute size differed from previous observations, and even though subjects had never seen the machine generate objects of the required size before. This suggests that children quickly inferred abstract causal relations and then generalized these relations to determine which intervention would bring about the novel outcome required to solve the problem. These findings suggest a close link between early relational reasoning and active causal learning and inference.
