As adults, we readily work through alternative possibilities and their potential consequences in our minds before acting. This capacity for mental simulation enables us to internally explore alternatives without incurring costs of acting in reality. Young children are highly exploratory in the real world, but little is known about their ability to engage in internal exploration via mental simulation. This preregistered study (1) examines developmental changes in the use of mental simulation when solving problems with multiple options, and (2) investigates the influence of resource availability on the tendency to simulate. Adults (N=30) and 4-to 7-year-olds (target N=120; data collection ongoing) completed computer-based puzzles where they chose where to drop balls into a vertical maze to hit a goal. Accuracy and latency to act were measured as indices of mental simulation. Our findings will contribute to understanding children's problem-solving, and could lead to a new conceptualization of their exploratory behaviour.

Toddlers can learn cause-effect relationships between single actions and outcomes. However, real-world causality is often more complex. We investigated whether toddlers (12- to 35-month-olds) can learn that a sequence of two actions is causally necessary, from observing the actions of an adult demonstrator. In Experiment 1, toddlers saw evidence that performing a two-action sequence (AB) on a puzzle-box was necessary to produce a sticker, and evidence that B alone was not sufficient. Toddlers were then given the opportunity to interact with the box and retrieve up to five stickers. Toddlers had difficulty reproducing the required two-action sequence, with the ability to do so improving with age. In Experiment 2, toddlers saw evidence that performing a single action (B) was sufficient to produce an effect (i.e., a sequence was not causally necessary). Toddlers were more successful and performed fewer sequences in Experiment 2, suggesting some sensitivity to the sequential causal structure.

To investigate the role of ostensive cues in pedagogical reasoning, we explored whether toddlers, like preschoolers, would copy causally implausible actions following a pedagogical demonstration. Toddlers watched a demonstrator perform a two-action sequence (AB) on a puzzle-box that led to a reward. We manipulated the demonstrator’s intentionality and the causal plausibility of action A and examined how these factors influenced copying behavior. Although toddlers were more likely to copy A when it was causally plausible, they were not influenced by the demonstrator’s intentionality. Importantly, toddlers were no more likely to copy the AB sequence following a pedagogical demonstration vs. a non- communicative demonstration. Comparing behavioural data to computational model predictions for learners differing in their sensitivity to intentionality and causal plausibility supported an absence of pedagogical reasoning. These results suggest that sensitivity to ostension may be a necessary prerequisite—but is not sufficient for—pedagogical reasoning in a causal imitation task.