Sydney  - Sending fat children to see doctors is not making them any thinner, exercise more or eat healthier food, researchers said Friday.

The findings, from Melbourne's Children's Research Institute, have just been published in the British Medical Journal.

They are a worry given that 30 per cent of Australian children are overweight, compared with 20 per cent 10 years ago and 10 per cent in 1994.

Researchers led by Melissa Wake split a group of 250 overweight children aged 5-9, with one half receiving no intervention and the other half given 12 weeks of sessions with doctors about diet and exercise.

A year on, they found no appreciable weight difference in the two groups.

"Effective solutions remain elusive, even when obesity is identified," Wake said. "It's time for real and immediate political and public health action to manage childhood obesity."

She said it was worth trying to get in early because fat children become fat adults and have more than their fair share of sickness, sadness and health care costs. (dpa)