Yet studies show that both food preferences and the foundations of chronic conditions such as obesity and blood pressure are laid down before the age of five.
A recent report from the University of Bristol even suggested that an unhealthy diet in these early years was linked to lower IQs, while a diet full of vitamins and nutrients could boost IQ.
With more than 600,000 children under five in daycare, often for 10 hours a day, many end up eating more meals in their first few years inside a nursery or Children's Centre than they do at home.
So making sure what goes into your child's tummy when they're out of sight is vital.
Too much salt, sugar and fat
Last year a School Food Trust report suggested that food served by childminders and nurseries is too high in fat, sugar and salt, and lacks essential nutrients. Now many are calling for more official guidelines and regulations for nursery nutrition.
So what should you look for as a parent and how can you help make sure your child's nursery is feeding them properly? Here with the help of top TV nutritionist Nigel Denby, from www.grub4life.org.uk, we've put together 10 top tips to help.
He says: "You have a right to expect that your child is being fed properly, especially since many parents are paying good money for their nursery place. The main thing is – don't be afraid to ask."
1. What should you expect?
Nigel says: "A child's diet should ideally consist of three meals a day and two snacks. A one to two-year-old should be having around 1100 calories, a three to four-year-old 1480 calories a day. There should always be a main course and dessert served. But, as well as getting too much, there is the danger that they don't get enough energy from carbohydrates. Ask if there are second helpings available. Children are pretty good judges of when they are full."
2. Ask for a menu plan.
Nigel says: "Ask to see a forward plan for the weeks ahead of what will be served at every meal. Many nurseries already do this. The main thing you should be looking for is plenty of variety with things like fish and red meat included. Is there a vegetarian day? Your nursery should be able to tell you how frequently they serve these foodstuffs. Look out for duplication. If lunch is a diary rich meal like a creamy pasta for example, is tea very different?"
3. Processed or fresh?
Nigel says: "Look for how much of the food is processed, like chicken nuggets, baked beans, and pastry based products as opposed to made from scratch using fresh ingredients. Some foods like sausages or pre prepared meat products should only be served once or twice a week. Many nurseries have a no added salt policy. But a lot of salt can be hidden in stock cubes and gravy granules?
4. Too much fruit?
Nigel says: "Fruit should be readily available but many nurseries serve fruit at every meal for dessert. Fruit all the time does not provide enough calories for the under fives and needs to be combined in a menu with other desserts such as rice pudding.
5. Watch out for treats.
Nigel says: "Children at nurseries can end up eating too much sugar. It tends to be someone's birthday pretty often – with celebratory, sugary cakes served up. Encourage your nursery to serve healthy party menus with things like banana bread rather than products with lots of saturated fat."
6. Do the nursery staff eat with the children?
Nigel says: "Children learn about food from adults eating with them - it is considered good practice for staff to eat with children. The children should be encouraged to use spoons and cutlery for their development."
7. Visit a mealtime
Nigel says: "The best way to judge your child's nursery meals is to ask if you visit the nursery at a meal time. How is the food presented? Do the children get involved with laying the table? These are both good indicators of the overall standard of food."
8. What's the food culture?
Nigel says: "Does the nursery use food in play and other activities – growing vegetables in grow bags for example. It's good practice to let children experiment with foods in non eating environments."
9. Is there a special diets policy?
Nigel says: "What is the nursery's policy on special diets for food allergies or vegetarian children - many nursery staff and cooks receive no training to cater for special diets."
10. Are there any guidelines to help parents?
Nigel says: "The Caroline Walker Trust has produced comprehensive guidelines for the food served to children in child care. You can view them and menu recommendations at www.grub4life.org.uk."
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