Children learn causal relationships quickly, and make far-reaching causal inferences on the basis of what they see. In order to be such efficient learners, they must bring abstract knowledge to bear on their problems. This paper addresses children's ability to acquire that knowledge. We present evidence that children can learn about the abstract properties of causal relationships using only a handful of events, and –- consistent with a hierarchical Bayesian model of casual inference –- children can be more sensitive to evidence than adults.