Minority and low-income children are overrepresented among obese US children. Lack of basic nutrition knowledge among parents may contribute to this disparity. The purpose of this study is to measure nutrition knowledge of parents of Medicaid-insured obese children using a simple low-literacy tool. Parents, recruited from pediatric clinics, demonstrated their nutrition knowledge by placing food stickers into cells on a printed grid with food groups displayed in columns and three nutrition categories displayed in rows. In general, parents (n = 135; 74.8 % black; 79.2 % income of ≤$25,000/year) correctly identified food groups (median = 90.5 % correct). Nutritional categories were more commonly misidentified (median = 67 % correct), with parents mostly believing foods were healthier than they were. Multivariable linear regression revealed black race (p = 0.02), no college education (p = 0.02) and income of <$15,000 (p = 0.03) independently predicted misidentification of nutritional categories. Parents' understanding of food's nutritional value is variable. Black race, less education, and very low income are associated with poorer nutrition knowledge.