This study examined the development of uncertainty monitoring in early childhood. Specifically, this study tested the prediction that preschoolers can reflect on their sense of certainty about the likely accuracy of their decisions, and it examined whether this ability differs across domains. Three-, 4-, and 5-year-olds (N = 74) completed a perceptual identification and a lexical identification task in which they reported whether they were certain or uncertain about their answers. Results showed that even 3-year-olds provided confidence judgments that discriminated accurate from inaccurate responses, but this discrimination increased with age. Furthermore, results suggest that 3-year-olds primarily rely on response latency to assess certainty, whereas older preschoolers do not. Overall, these findings suggest that uncertainty monitoring emerges and develops during the preschool years.