But a BBC Panorama investigation into food for the under-fives found that easy answers to healthy eating can be as hard to come by as a full night's sleep and a long lie.

For the parents of the 1.5m children who regularly attend nursery in the UK, the nutritional puzzle is even harder to piece together. While celebrity chef Jamie Oliver successfully raised the profile of the importance of nutritional standards being met in school dinners, Scotland is the only place where similar set guidelines apply to nursery food.

Patchwork policies

In England, government advice for care of children aged one to five states they should be eating a "healthy, balanced and nutritious" diet, but does define what that diet should contain. England's strict nutrient-based standards for primary schools do not apply in pre-school settings.

Northern Ireland does not use nutrient based standards at all and in Wales they are being piloted for schools, and are recommended for early years.

As part of an ongoing study of nursery food across England, Trading Standards in Hampshire surveyed the food at 10 nurseries that volunteered to take part.

They found that while the nurseries were doing well in keeping salt levels low, none of them were providing enough fat or energy in their meals.

Sue Powell of Hampshire Trading Standards said the focus on fruit and vegetables - key to a healthy adult diet - omits the reality that growing toddlers need a higher fat diet.

"I think the perception is that maybe giving the children too much fat is actually a bad thing and we forget that children do actually need fat, they need carbohydrate and they need protein to actually give them the energy that they need."

Not enough energy

The survey - the national results of which are due to be released next month - found that most nurseries were not serving enough oily fish and none were providing enough zinc in their meals.

Jacqui Horton of Woodlands Nursery - one of those in the initial findings in Hampshire - said the message of 'five a day' had gotten through loud and clear, but the survey found that they had not been giving the toddlers enough carbohydrate.

"The plate was being filled with those five fruit and veg for their pudding and their main, and we weren't putting enough energy on. The energy was on the plate, but just not enough of it."

Professor Terry Wilkin of Peninsula College of Medicine in Plymouth has studied the impact of poor diet in the under-fives and warns that all the attention on keeping school age children fit and healthy - from healthier meals to cutting down on television and screen time to after school physical activities - could be missing the age group where it matters the most.

"These are not factors that operate in a two-year-old's life and yet the evidence is from other studies that it may even be younger than two years old that this weight gain begins to occur."

Fussy eaters


 
There are calls for easy-to-read labels on food marketed for children
In their search for the best possible nutritional mix for their children at home, many parents have turned to kiddie food guru Annabel Karmel for help with recipes and diet plans.