Summary Approximately 1 in 3 children in the US experience neglect and/or abuse (“maltreatment”) before they turn 18 years old, with marginalized racial and ethnic communities and young children facing the greatest risks. For the past century, research has treated maltreatment largely as a failing of individual parents, despite robust evidence that maltreatment risk, particularly for neglect and physical abuse, is powerfully shaped by structural determinants such as poverty and stress. Population-level maltreatment prevention could have major public health impacts, but it is not yet clear how to prevent maltreatment at scale. Emerging research suggests that economic and social welfare policies that alleviate financial hardship and reduce stressors for families could potentially serve as population-level prevention interventions. However, two major gaps limit the utility of the existing evidence base for identifying policies with the potential to prevent maltreatment. First, prior research has evaluated individual policies one at a time without accounting for the ways that changes in one safety net policy may affect the eligibility for and benefits from others. This failure to account for policy interactions may result in mis-estimation of overall safety net benefits and mis-attribution of effects of one policy to another. Second, prior research has almost exclusively assessed maltreatment through Child Protective Services (CPS) involvement (e.g., reports of maltreatment to CPS), and thus impacts on other critical public health outcomes such as maltreatment-related injuries remain unknown. The overarching goal of this research is to identify the impact of social safety net policies on CPS reports and injuries related to neglect and physical abuse in young children. Two key innovations will directly address current knowledge gaps. First, to estimate benefits from each major social safety net program (EITC, CTC, SSI, TANF, SNAP/WIC, and Medicaid/CHIP), accounting for other programs, we will use and expand a safety net benefits calculator. This calculator sequentially applies program rules for each state and year, allowing benefits from one program (e.g., TANF) to be incorporated into eligibility and benefits estimates for others (e.g., SNAP), as dictated by program rules. Second, we will combine and harmonize over 300 state-years of data on ED and inpatient visits for pediatric injuries that are highly correlated with maltreatment. We will estimate the impact of social safety net policies on these maltreatment-related injuries in addition to CPS reports. We will focus on young children (aged <5 years) as they are at greatest risk of maltreatment. We will also examine these outcomes by race and ethnicity to determine impacts on equity. The aims of our research are to: (1) Estimate the effect of major social safety net policies (EITC, CTC, SSI, TANF, SNAP/WIC, Medicaid/CHIP) on CPS reports of neglect and physical abuse in young children (age <5 years)...