Aiming to examine social norms regarding secondborn's sharing behaviour after the reversal of the one-child policy, three studies were conducted to explore preschoolers' sharing behaviours (Study 1, n = 88); their evaluations (Study 2, n = 93); and adults' evaluations (Study 3, n = 535) of younger siblings' sharing behaviour toward their older siblings, good friends, and strangers. The results showed that secondborn preschoolers tended to share more with older siblings and good friends than with strangers, while being indifferent to or making no distinction between older siblings and good friends. However, both preschoolers and adults tended to be more tolerant if secondborn preschoolers shared less with older siblings than with strangers or good friends. Overall, these findings suggest that the traditional norm of 'older gives way to younger' persists as a social norm in contemporary China, despite the growing emphasis on sibling interactions and fairness in sibling sharing.