Developmental trajectories and individual differences in 70 American middle-income 2.5- to 4-year olds' moral judgments were examined 3 times across 1 year using latent growth modeling. At Wave 1, children distinguished hypothetical moral from conventional transgressions on all criteria, but only older preschoolers did so when rating deserved punishment. Children's understanding of moral transgressions as wrong independent of authority grew over time. Greater surgency and effortful control were both associated with a better understanding of moral generalizability. Children higher in effortful control also grew more slowly in understanding that moral rules are not alterable and that moral transgressions are wrong independent of rules. Girls demonstrated sharper increases across time than boys in understanding the nonalterability of moral rules.