To become cooperative members of their cultural groups, developing children must follow their group's social norms. But young children are not just blind norm followers, they are also active norm enforcers, for example, protesting and correcting when someone plays a conventional game the "wrong" way. In two studies, we asked whether young children enforce social norms on all people equally, or only on ingroup members who presumably know and respect the norm. We looked at both moral norms involving harm and conventional game norms involving rule violations. Three-year-old children actively protested violation of moral norms equally for ingroup and outgroup individuals, but they enforced conventional game norms for ingroup members only. Despite their ingroup favoritism, young children nevertheless hold ingroup members to standards whose violation they tolerate from outsiders. (Contains 3 figures and 3 tables.)