The dysregulation of social fear has been widely studied in children's shyness, but we know little about how shy children regulate during unfair treatment. We first characterized developmental patterns of children's shyness (N = 304, n  = 153; 74% White, 26% Other) across 2 (M  = 2.07), 3 (M  = 3.08), 4 (M  = 4.08), and 6 (M  = 6.58) years of age. Data collection occurred from 2007 to 2014. At age 6, the high stable group had higher cardiac vagal withdrawal and lower expressed sadness and approach-related regulatory strategy than the low stable group when being treated unfairly. Although shy children may be more physiologically impacted by being treated unfairly, they may mask their sadness to signal appeasement.