Although some evidence indicates that even very young children engage in rudimentary forms of strategic behavior, the underlying mechanisms remain largely unknown. This study tested the hypothesis that uncertainty monitoring underlies such behaviors. Three-, four-, and five-year-old children (N = 88) completed a perceptual discrimination task. Results indicated that children are more likely to withhold (vs. volunteer) responses on trials for which, when forced to provide an answer, they report subjective uncertainty (vs. subjective certainty). Furthermore, uncertainty monitoring positively predicted the strategic regulation of accuracy via withholding of incorrect responses, even when controlling for individual differences in inhibitory control. Overall, results suggest that children's awareness of their own knowledge states contributes to early strategic behavior.