In adults, heightened self-awareness leads to adherence to socially valued norms, whereas lowered self-awareness is associated with antinormative behavior. Levels of self-awareness are influenced by environmental cues such as mirrors. Do situational changes in self-awareness also have an impact on preschoolers' self-regulation? Adherence to a socially valued standard was observed under different conditions of self-focus. In Experiment 1 the standard was prescribed ("don't look in the box"), and in Experiment 2 children had the opportunity to be altruistic. Heightened self-focus was induced using a large mirror. In a neutral condition, the nonreflective side of the mirror was shown. To lower self-focus, children wore a disguise. Preschoolers peeked less and showed more altruism when the mirror image was present. As found for adults, it appears that self-awareness leads 3- and 4-year-olds to adhere to salient social standards. These results suggest that self-focus has a socially adaptive regulatory function from an early age. (Contains 4 tables.)