In this study, we explore how default options affect the inferences that children draw and whether they can use them effectively to influence others. Do children infer that a decision maker has a stronger preference for an option when it requires switching from the default (rather than staying with the default)? And can children set optimal defaults to influence others to choose a particular option? These two-in-one studies help advance our understanding of how children reason about the mental states of social agents and its developmental trajectory.