PROJECT SUMMARY/ABSTRACT The family unit is an important yet understudied point of intervention that can be leveraged to promote critical understandings about fairness, foster empathy and cooperation with others, and reduce harmful anti-social behaviors (e.g. bullying, harassment) among young children. Teaching and socialization practices among caregivers are critical to support prosocial behaviors, such as encouraging positive peer relationships and interactions, which have been shown to improve social/emotional well-being among children. This project is innovative by focusing on practices that families can engage in to encourage prosocial behaviors and prevent the perpetration of those that are harmful, which have been shown to benefit all children. We will recruit a national sample of primary caregivers and their K-2nd grade children. Qualitative data from focus groups will enhance the scientific basis for our intervention program—a multi-module app that guides parents in having conversations with their children about treating others fairly, resolving conflict, and principles of cooperation, and provides strategies on how to foster empathy. We test the intervention using a rigorous randomized attention/wait-list controlled trial design. The design of the intervention is based on research indicating that among children, positive intergroup contact with outgroup members, including vicarious engagement, can prevent or reduce anti-outgroup behaviors particularly when contact is based on common goals, cooperation rather than competition, and supported by external authorities. We collect a broad range of measures using mixed-methods, through one-one-one interviews with caregivers and children and dyadic interviews. Adapting the intervention for delivery via a downloadable app facilitates scalability resulting in greater potential to have wide social impact. This work expands the scope of the science on how teaching and socialization practices within families can enhance children’s developmental and health outcomes.