Nutritionists say applying the principles of adult healthy eating to young children can lead to vitamin deficiencies and even stunted growth.
According to consultant paediatric dietician Dr. Sarah Almond, who has analysed the results of a Trading Standards study into nursery food, a diet high in fibre and low in fat, with plenty of fruit and vegetables is unsuitable for toddlers.
Dr. Almond says the expectation was that the research would show nurseries were serving children food that was too high in calories, fat, saturated fat and salt, and low in vegetables and fruit.
But in fact the opposite was true and the majority of nurseries had gone to the other extreme and appeared to be providing food that was too low in calories, fat and saturated fat and too high in fruit and vegetables.
She says such a regime puts children at risk of developing nutritional deficiencies.
The research also revealed that most nurseries were serving children portions which were too small and very few provided them with meals containing enough calories.
Dr. Almond says the under-five age group has different and specific nutritional requirements to children of school age because they have a high energy and nutrient requirement.
They also have small stomachs and relatively under-developed guts and cannot consume large quantities of food at a time but need frequent small meals and snacks throughout the day.
Too much fibre such as that absorbed through over-consumption of fruit and vegetables can result in insufficient intake of other food groups and inhibit the absorption of key minerals.
Almond says because many children attend nurseries from 7am until 7pm, the food and nutrition they receive there are essential to their health.
Unlike school meals, government regulations do not apply to the provision of toddlers' meals and nurseries are only offered general advice which suggests childcare agencies refer to the Food Standards Agency for advice on food and nutrition for young children.
Experts say many nurseries are confused or misinformed about what entails healthy eating for the under-five age group and the nutritional content of toddlers' meals is a proper science.
They say nurseries are unaware of vital calories, fats, carbohydrate, sugars, fibre, protein, vitamins and minerals and the nutritional requirements for this particular age group.'