Children with callous-unemotional (CU) traits are at high lifetime risk of antisocial behavior. Low affiliation (i.e., deficient motivation for social bonding) and fearlessness (i.e., reduced sensitivity threat) have been proposed as risk mechanisms that contribute to the development of CU traits. Parenting practices (e.g., harshness and low warmth) also predict risk for CU traits across childhood. However, no work in early childhood has identified attentional or physiological markers of low affiliation and fearlessness nor examined associations with later CU traits. Moreover, no studies have tested whether parenting practices are underpinned by low affiliation or fearlessness shared by parents, which could shape parent-child interactions and exacerbate risk for CU traits. Addressing these questions will inform knowledge of how CU traits develop and help to isolate novel parent and child targets for future specialized treatments for CU traits. The Promoting Empathy and Affiliation in Relationships (PEAR) study aims to establish risk factors for CU traits in 3-6-year old children. The PEAR study will recruit 500 children and parents at ages 3-4 (time 1) and ages 5-6 (time 2). Measures will include parent-reported questionnaires, computer tasks, and observation, combined with eye-tracking and physiological assessments, to facilitate a multi-method investigation of low affiliation, fearlessness, and parenting practices as risk factors for CU traits. The PEAR study will also investigate the moderating roles of child gender and race/ethnicity, family and neighborhood instability or disadvantage, and parental psychopathology. Study aims will be addressed within a structural equation modeling framework, which will flexibly leverage the multi-modal, multi-level assessment strategy. Ethics and dissemination. Ethical approval was granted by Boston University (#6158E) and the University of Pennsylvania (#850638). We will disseminate results through conferences and open access publications. All study and task materials will be made freely available.