The purpose of the study was to examine the influences of age, family socio-economic status (SES), and parents' food knowledge on preschool, kindergarten, and second grade students' conceptual understanding of food and nutrition. Fifty-two parent-child dyads, consisting of 17 preschoolers, 17 kindergartners, and 18 second graders participated in the study. Parents completed a self-administered survey at home and the children were interviewed at school sites. We found the significant age effects on children's conceptual understanding of food. Specifically, significant differences were found in total food knowledge between preschool and second-grade students, the food-body and food-fat knowledge scores between preschool and second grade students, and between kindergarten and second grade students. SES family background had no significant impact on children's conceptual understanding of food. No clear correlation was found for food knowledge between children and their parents.