OBJECTIVE In the early years of life, influential attributes are formed and may be difficult to change later in life. Early childhood is now recognised as a key target in the prevention of overweight and obesity, and the knowledge that children gain at this time about food and its health benefits may have an important influence on their dietary choices and preferences in later life. Therefore, an activity was designed using age-appropriate methods to assess nutrition knowledge of young children. DESIGN The Healthy Food Knowledge Activity was developed using a list of thirty healthy and unhealthy foods and drinks generated from the Australian Guide to Healthy Eating. SETTING The activity was conducted with individual children from reception classes of South Australian schools. SUBJECTS Children aged 5-6 years undertook the activity in a pilot study (n 13) and in the main study (n 192). RESULTS Pilot data indicated good test-retest reliability of the activity (r = 0·84, P < 0·01). In the main study, there was a good distribution of scores with acceptable skewness and kurtosis statistics. A breakdown of responses indicated good face validity, with more obvious foods being more correctly classified. CONCLUSIONS Children as young as 5-6 years of age can correctly identify healthy foods, and this can be measured objectively. This activity also provides interesting insights regarding misconceptions about foods that could be attributed to influences such as media advertising and that can be addressed by educators of this age group.