This review addresses epidemiological, public health, and social policy implications of categorizing young children and their adult female caregivers in the United States as food secure when they live in households with "marginal food security," as indicated by the U.S. Household Food Security Survey Module. Existing literature shows that households in the US with marginal food security are more like food-insecure households than food-secure households. Similarities include socio-demographic characteristics, psychosocial profiles, and patterns of disease and health risk. Building on existing knowledge, we present new research on associations of marginal food security with health and developmental risks in young children (<48 mo) and health in their female caregivers. Marginal food security is positively associated with adverse health outcomes compared with food security, but the strength of the associations is weaker than that for food insecurity as usually defined in the US. Nonoverlapping CIs, when comparing odds of marginally food-secure children's fair/poor health and developmental risk and caregivers' depressive symptoms and fair/poor health with those in food-secure and -insecure families, indicate associations of marginal food security significantly and distinctly intermediate between those of food security and food insecurity. Evidence from reviewed research and the new research presented indicates that households with marginal food security should not be classified as food secure, as is the current practice, but should be reported in a separate discrete category. These findings highlight the potential underestimation of the prevalence of adverse health outcomes associated with exposure to lack of enough food for an active, healthy life in the US and indicate an even greater need for preventive action and policies to limit and reduce exposure among children and mothers.