The first food guidelines for nursery-age children are being introduced by a childcare charity concerned that poor eating patterns, which can lead to obesity, are laid down by the time youngsters are five.

The pre-school learning alliance, whose member pre-schools care for 500,000 children in England, is to issue dietary guidance for its own nurseries and for parents bemused by competing nutritional advice and scare stories.

The charity is working with the British Nutrition Foundation to develop the Feeding Young Imaginations campaign, which will reflect the differing needs of babies, toddlers and young pre-school children.

Campaigners began the work after it emerged that, despite the wealth of nutritional guidelines aimed at schools, no comparable requirements existed for younger children.

The issue is becoming more acute for pre-school groups, since government moves towards extended day care mean pre-schools are now much more likely to be providing lunch and running breakfast clubs, as well as serving break-time snacks.

The alliance, whose annual conference takes place today in London, points to statistics predicting that, under current trends, more than 40% of the UK could be obese within a generation.

Its chairwoman, Judith Thompson, said: "Starting nutritional advice only at school age, five to 16, is far too late, because your eating preferences, like so many other things, are established in the early years."

The alliance wanted to provide practical guidance for pre-schools and parents that helped them provide a balanced and healthy diet for babies and children "without creating rods for parents' backs", she added.

"We want them to have the confidence to say no to their children while having something else up their sleeve, which they might have fun making together."