PROJECT SUMMARY One in four children in the United States (US) has at least one immigrant parent—more than a third of whom came to the US from Mexico more than any other country of origin. Children of Mexican immigrants, in particular those without documentation status, are exposed to psychosocial stress through their parents and yet, nationally-representative analyses of how structural factors affect child dietary acculturation or obesity. Mexican American children/adolescents experience disparities in obesity as compared to either their non- Hispanic Whites or Mexican peers. The tapestry of state and local level immigration policy climates in the US provides an opportunity to study their impact on immigrant families, both short and long-term. We will address this research gap, by analyzing a novel data set of immigration policy climates linked to nationally- representative data, to apply quasi-experimental and longitudinal methods. Aim 1 will study how the Illegal Immigration Reform and Immigrant Responsibility Act Section 287(g), a local-federal immigration enforcement program, initiation affects measures of child diet and obesity in the year following implementation, as compared to the same locality the year prior to implementation. Then Aim 2 will expand the focus to include other immigration enforcement programs (e.g. Secure Communities) and types of immigrant inclusion/exclusion in state level policies (e.g. public health and welfare benefits, higher education, employment, and identifications) across 10 years. We focus on children of Mexican immigrants given their obesity disparities and demographic importance, but also compare our results to children of other immigrants, US-born Mexican Americans and other US-born parents. Anticipated findings of this work will advance our understanding of population-level structural determinants of obesity in Mexican American children, before weight trajectories have been set or comorbidities arise, and may inform public health interventions for this vulnerable population.