Ministers must do more to protect pupils from primary school dinners high in fat and salt, a report says.
The government says it is monitoring primary school meals
The Soil Association, which promotes organic farming, said it had analysed five typical lunches.
Children eating such meals every day would consume 40% more salt, 28% more saturated fat and 20% more sugar than recommended, it said.
The Department of Education said it had started a monitoring exercise to check the quality of food served in primary schools.
The warning comes amid widespread concern over childhood obesity.
'Not enough nutrients'
A "typical" school meal including cheese fritters, roast potatoes, peas and flapjacks would only provide 80% of the amount of iron and 70% of the amount
of zinc needed, the Soil Association said.
Education Secretary Charles Clarke recently announced he would review the standard of dinners served in secondary schools.
But the Soil Association, said it wanted him to act on primary schools too.
Peter Melchett, the group's policy director, said: "It is well
known that most school dinners in primary schools do not provide the correct level of nutrients and give children too much fat, sugar and salt.
"But still Charles Clarke refuses to act to protect children at their most crucial stage of development.
"If children are encouraged to eat healthily in primary school, they are likely to demand good quality food as they get older."
A Department for Education and Skills spokeswoman said work was already under way to improve the quality of school meals.
She added: "We are also undertaking a specific monitoring and evaluation exercise on the quality of primary school meals.
"We are determined to ensure young people are inspired to eat and live healthily."