The ability to experience uncertainty (i.e., uncertainty monitoring) is an important skill that enables us to optimize our performance by acting cautiously or seeking additional information when we feel uncertain, and by expressing our knowledge when we feel certain (i.e., uncertainty control). Research reveals that even young preschoolers can introspect on uncertainty and act appropriately based on these introspections. We conclude that uncertainty monitoring and control can be driving forces of cognitive development during the preschool years. In this article, we review the emerging literature on this topic, highlight open questions, and draw connections with other research domains.