The survey of 27,500 children aged five to 16, which claims to be the largest poll of its kind, also reveals that over a third of five to eight-year-olds think pasta comes from animals.
One in ten secondary school children believe that tomatoes grow under the ground.
The research, conducted by the British Nutrition Foundation (BNF) to coincide with their Healthy Eating Week (3-7 June), also asked children about their eating habits.
According to the BNF, 16 per cent of primary children said they never eat fish and six per cent reported not eating breakfast every day.
While over three-quarters (77 per cent) of primary children knew they should eat five portions of fruit and vegetables a day, 67 per cent reported eating less than four portions.
The survey also shows that 17 per cent of primary school children cook every day or once a week, although nine per cent never cook at home.
Despite this, 84 per cent of primary school children said they would like to cook more, and an average of 85 per cent of children across all age groups said they enjoy cooking.
Over 3,000 schools and nurseries are expected to take part in this week’s Healthy Eating Week, which was launched by the Princess Royal.
The aim of the week is to promote healthy diets and being more active, as well as improve children’s understanding of where food comes from.
Roy Ballam, education programme manager at the British Nutrition Foundation, said, ‘Schools throughout the UK require a national framework and guidance for food and nutrition education to support the learning needs of children and young people, especially at a time when childhood obesity is soaring.
'Through Healthy Eating Week, we hope to start the process of re-engaging children with the origins of food, nutrition and cooking, so they grow up with a fuller understanding of how food reaches them and what a healthy diet and lifestyle consists of.’
He added, ‘Through this survey one in five (21 per cent) primary school children and 18 per cent of secondary school pupils told us that they have never visited a farm. This may go part way to explaining why some children believe pasta comes from animals.’
Libby Grundy, director of the Food for Life Partnership, which works with schools to develop children's undertanding of where their food comes from, said, 'We know some children and families are becoming detached from how their food is produced and don’t always have the skills and knowledge needed to take active control over what they eat. The British Nutrition Foundation survey reinforces the urgent need for the Government to support programmes that are already actively addressing these issues.'