Young children robustly distinguish between moral norms and conventional norms (Smetana, 1984; Yucel et al., 2020). In existing research, norms about the fair distribution of resources are by definition considered part of the moral domain; they are not distinguished from other moral norms such as those involving physical harm. Yet an understanding of fairness in resource distribution (hereafter, "fairness") emerges late in development and is culturally variable, raising the possibility that fairness may not fall squarely in the moral domain. In 2 preregistered studies, we examined whether U.S. American children who were primarily White see fairness as a moral or conventional norm. In study 1 (N = 96), we did not obtain the established moral-conventional difference needed to investigate questions about the status of fairness. We improved our design in our second preregistered study. In study 2 (N = 94), 4-year-olds rated moral transgressions (e.g., hitting) as more serious than fairness and conventional transgressions (e.g., wearing pajamas to school), but importantly, they rated fairness and conventional transgressions as similarly serious. In contrast, 6- and 8-year-olds rated moral transgressions as more serious than fairness and conventional transgressions, and fairness as more serious than conventional transgressions. An additional, forced-choice procedure revealed that most 6-year-olds also categorized fairness with moral rather than conventional transgressions; 4- and 8-year-olds' responses on this measure did not show systematic patterns. U.S. American children may not equate norms of fairness in resource distribution with harm-based moral norms, even into middle childhood.