A survey on English nursery schools has found that too much fruit and inadequate carbohydrate is being fed to kids and this may not be enough to maintain their energy levels.
Children are also given too much salty food, and the size of portions varies: some are big enough for 10-year-olds and others so small that they lack key nutrients.
Parents are also blamed for putting pressure on staff to ban key sources of nourishment such as whole-fat milk and red meat.
The findings are released today by the Local Authority Co-ordinators of Regulatory Services (LACORS), which asked trading standards officers in 29 councils, including Cumbria, Hampshire and Leicestershire, to check on the lunches and snacks offered by 118 nurseries over a five-day period.
The results provide a nationwide snapshot of the food offered to more than 600,000 children who spend up to ten hours a day at nursery.
One surprise is the lack of food in mid-morning and the afternoon. Some children received only half an apple or pear to keep them going until lunch. In the afternoon some were not offered a snack at all, and for those that were, it was often banana pieces or grapes.
There was no evidence of children starving and most nurseries tried to offer a good diet.
However, too many meals were based on ham, sausages and other processed meat. Overuse of packet mixes for gravy and other sauces were blamed for the high salt content of meals.
Some nursery schools were also criticised for serving too much bread, and others for excessive use of cheese, which can be high in salt.
Too many lunch plates were also short of green vegetables, pulses, eggs, oily fish and red meat, which are good sources of iron, zinc and calcium for a child.
Council chiefs now want guidance for nurseries, childminders and parents on suitable food.
"Most people assume it's all about beating obesity, but nutrition problems can also be caused by not giving children enough of the types of food they need," the Times quoted Paul Bettison, LACORS chairman, as saying.
"For many adults, drinking skimmed milk, eating no red meat and loads of fruit is wonderful, but it's not what a growing body needs," he said.
Most nursery schools were independent, he said, and if parents were unhappy, they would move their children.
"Nurseries have a dilemma - do they do what they know is right or do they do what parents think is right? A diet for mum and dad is not the diet for a three-year-old. Parents need to be taught what is best for their children," he stated.
"This highlights the need for new guidance for under-5s," Helen Crawley, of City University, London, director of the Caroline Walker Trust, which promotes good diet, said.
"But it depends on each child, how long they spend in a nursery and what they eat at home. I am part of an advisory group to make recommendations to the Government by the summer," she stated.
The Basingstoke College of Technology nursery was giving children insufficient carbohydrate but has changed its snacks to fruit or carrot sticks plus crackers, bread sticks, toast, oatcakes, scones, flapjacks, cheese cubes, houmus or fromage frais.