Children have an early-emerging expectation that resources should be divided fairly amongst agents, yet their behavior does not begin to align with these expectations until later in development. This dissociation between knowledge and behavior raises important questions about the mechanisms that encourage children to behave how they know they should behave. Here I tested whether explicitly invoking fairness norms encourages costly fair decisions in 4- to 9-year-old-children. I examine children’s responses to unequal resource allocations in the Inequity Game by varying the direction of inequity (advantageous versus disadvantageous inequity) and normative information (to be fair or to act autonomously). The results show children are more likely to reject advantageous allocation in the Fairness norm condition than in the Autonomous norm condition, but I did not see this difference when children are presented with disadvantageous allocations. This study showcases children’s costly fairness norm enforcement as a flexible process, one that can be brought in and out of alignment with their knowledge of fairness by shining a spotlight on how one ought to behave.