Upon witnessing a causal event, do children's gestures encode causal knowledge that (a) does not appear in their linguistic descriptions or (b) conveys the same information as their sentential expressions? The former use of gesture is considered supplementary; the latter is considered reinforcing. Sixty-four English-speaking children aged 2.5-5 years described an action in which the experimenter pushed a ball across a small pool with a stick. Over time, children produced more complete sentences expressing causal relations, encoding more of the elements in the event. Younger children produced noncausal sentences and location gestures that referred to or highlighted the goal of the action. Older children used both reinforcing and supplementary gestures conveying the instrument (e.g., the stick) and direction (e.g., from left to right) of the action. These findings present a noncausal to causal developmental trajectory both in speech and gesture. Among older children, results also suggest that gestures carry causal information before they form complete sentences to express causal events. (Contains 3 tables and 2 figures.)