Purpose To examine the interaction effects of adult and child food insecurity on parents’ and children’s mental well-being. Design An online survey study was conducted. Setting Two Head Start organizations and the Qualtrics Panel. Subjects Four hundred and eight parents under poverty level and having a child aged 3–5 years participated. Measures Food insecurity was assessed by the U.S. Household Food Security Survey Module. Parents’ stress, anxiety and depression; and children’s sadness, fear, anger, and positive affect were measured using instruments from HealthMeasures. Analysis Multivariate general linear models were performed in SPSS. Results Mean age was 31 years, 17% Hispanic, 21% Black. About 51% parents and 37% children were food insecure. After adjusting for demographics and child food insecurity, parents with adult food insecurity had higher stress ( B = 2.65, p = .002), anxiety ( B = 3.02, p = .001), and depression ( B = 3.66, p = .001); and fear in their children ( B = 5.03, p = .002) than those without adult food insecurity. Similarly, parents reporting child food insecurity had greater depression than those having no child food insecurity ( B = 4.61, p = .020). Black parents had lower stress ( B = −1.91, p = .018), anxiety ( B = −2.26, p = .012), and depression ( B = −4.17, p < .001) than their White counterparts. Conclusions The study’s results underscore the importance of reducing food insecurity in both parents and children as a whole family system to promote mental well-being of low-income families.