The emergence of disadvantageous inequity aversion between 2–4 years

When and how children begin responding to inequitable resource distributions, particularly those that put them at a disadvantage, remains unclear. Across two studies, an initial pilot experiment (N = 39) and a pre-registered follow-up experiment (N = 80), we employed modified versions of the Inequity Game to test implicit sensitivity and explicit response decisions to various disadvantageous offers in groups of 2- and 4-year-old children. Across experiments, both age groups showed evidence of sensitivity to disadvantageous offers that provided them nothing while their partner received resources (e.g. 0 vs. 3). However, only 4-year-olds were willing to forgo offerings involving personal gain (e.g., 1 vs. 3) to protest unfair treatment, a hallmark of disadvantageous inequity aversion. These findings suggest that sensitivity to disadvantageous offers emerges as early as the second year of life, but this sensitivity develops into disadvantageous inequity aversion over subsequent years.