BackgroundExisting research on the impacts of adversity on young children's psychological well‐being has largely focused on household‐level risk factors using observational methods in high‐income countries. This study leverages natural variation in the timing and location of community homicides to estimate their acute effects on the regulatory, behavioral, and developmental outcomes of Brazilian 3‐year‐olds.MethodsWe compared the outcomes of children who were assessed soon after a recent neighborhood homicide to those of children from the same residential neighborhoods who had not recently experienced community violence. Our sample included 3,241 3‐year‐olds (M_age = 41.05 months; 53% female; 45% caregiver education less than middle school; 26% receiving a public assistance program) from seven neighborhoods in São Paulo, Brazil. Child outcome measures included parent reports of effortful control and behavior problems as well as direct assessments of children's developmental (cognitive, language, and motor) skills. Community homicides were measured using police records.ResultsRecent exposure to community homicides was associated with lower effortful control, higher behavior problems, and lower overall developmental performance for children (d = .05–.20 standard deviations; p = ns – <.001). Effects were consistent across subgroups based on sociodemographic characteristics and environmental supports, but generally largest when community violence exposure was geographically proximal (within 600 m of home) and recent (within 2 weeks prior to assessment).ConclusionsResults highlight the pervasive effects that community violence can have on young children as well as the need to expand support to mitigate these effects and prevent inequities early in life.