Egalitarian behavior is considered to be a species-typical component of human cooperation. Human adults tend to share resources equally, even if they have the opportunity to keep a larger portion for themselves. Recent experiments have suggested that this tendency emerges fairly late in human ontogeny, not before 6 or 7 years of age. Here we show that 3-year-old children share mostly equally with a peer after they have worked together actively to obtain rewards in a collaboration task, even when those rewards could easily be monopolized. These findings contrast with previous findings from a similar experiment with chimpanzees, who tended to monopolize resources whenever they could. The potentially species-unique tendency of humans to share equally emerges early in ontogeny, perhaps originating in collaborative interactions among peers.