Although human societies provide protection from harm and enable the construction of collaborative and mutually beneficial social structures, they also pave the way for social hierarchies that deny equal treatment to certain portions of the population. Moral judgments about fairness and equality, as well as stereotypes, biases, and prejudice, emerge as early as 3 and 4 years of age. Investigating young children’s responses to the unfair treatment of others reveals that, beginning at 3–4 years of age, children often act on ingroup biases and do not yet challenge exclusion or rectify inequalities. By 5–6 years of age, however, children’s knowledge of groups, along with their understanding of others’ mental states, enables them to begin to critically evaluate unfair practices, particularly in peer contexts. These factors play a significant role in young children’s emerging ability to challenge unfair treatment of others.

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