Eating behaviours begin to develop during early childhood, but relatively little is known about preschoolers' nutrition knowledge. The current study examined age and gender differences in this knowledge using two tasks: food group classification and the creation of unhealthy, healthy and preferred meals. Sixty-nine three- to six-year-old children were interviewed. Findings suggest that the healthy meals children created were lower in calories and fat than their preferred and unhealthy meals. Older children and girls had a larger discrepancy in the calorie/fat content of their healthy and unhealthy meals than younger children and boys, respectively. Children's created meals showed some dietary variety, but many children could not provide valid explanations for why they selected the foods they did. Children were better at classifying fruits and vegetables than foods from the grain and dairy group. This study highlights the utility of using ecologically valid measures to understand children's developing nutrition knowledge. (Contains 4 tables.)