Latino children are the fastest growing population of obese children in the United States, the most obese group of children by race and a significant disparity in childhood obesity. Extended family, often grandparents, are traditionally involved in childcare in Latino family structure, yet their influence on family health behaviors is unclear. This study explored grandparent involvement in the care of Latino children in South Texas and their possible influence on child body mass index (BMI) and family health behaviors to determine if they present an opportunity to improve child obesity treatment plans. Partnering with the local school district, we surveyed parents (N = 174) and grandparents (N = 108) of 188 Latino, primary school-age children regarding grandparent care and family health behaviors. We weighed, measured, and interviewed children regarding grandparent care and their own health behaviors. All groups exceeded state and national obesity rates, with almost half the children in overweight or obese categories. Grandparents were routinely present in 30%-67% of the children sampled, dependent on respondent group. We found no significant relationship between grandparent involvement and child BMI, however grandparent cohabitation with the family was associated with less fast-food consumption by children (p = .001) and parents (p = .006) and healthier diet scores for children (p = .008) and grandparents (p = .004). More frequent exercise by parents (r = .33, p = .001) and grandparents (r = .25, p = .012) was associated with more frequent exercise by children. This study enhances understanding of grandparent involvement in the care of Latino children and illuminates opportunities to involve grandparents in family-focused, community-supported interventions, incorporating cultural understanding in decreasing Latino childhood obesity. (PsycInfo Database Record (c) 2021 APA, all rights reserved).