Children with siblings differ from only children in their sharing behaviour

China offers a natural laboratory for comparing the development of only children and children with siblings. We examined potential differences in the way that they expected a protagonist to allocate resources between two recipients with different social relationships, e.g. a sibling vs. a stranger, a friend vs. a stranger, and a sibling vs. a friend. Four- to six-year-old children participated in a third-party Resource Allocation Task and an Emotion Judgment Task. Children with siblings were more likely than only children to expect resources to be shared with a sibling over a friend. In addition, as compared to only children, children with siblings expected someone experiencing non-sharing behaviour to feel sadder. These findings suggest that the difference in kin-preference between children with siblings and only children is due to their respective life experiences.