Three-quarters of Australian children in their final year of primary school believe cotton socks come from animals and 27 per cent are convinced yoghurt grows on trees.

A national survey of year 6 and 10 students by the Australian Council for Educational Research found yawning gaps in young people's knowledge of basic food origins.

In a hypothetical lunch box of bread, cheese and a banana, only 45 per cent in year 6 could identify all three as from farms.

More than 40 per cent in year 10 thought cotton came from an animal and more than a quarter of their younger peers believed yoghurt came from plants. In year 10, 13 per cent identified yoghurt as a plant product.