The government is engaged in a battle for hearts and minds to persuade parents to join the fight against child obesity, the children's minister said today.

Soaring obesity called for a different kind of partnership between government, public services and families - with parents and children the most important part, Ed Balls said.

"The obesity crisis is happening before our eyes...Targets can help [tackle it] but in the end it's about persuading families and children they have to change the way they live," he told the Guardian Healthy Kids Summit.

A government-commissioned investigation into the scale of the obesity problem and what science can do to help tackle it is due out on Wednesday. The Foresight Report on Obesity is set to predict that half the population could be obese within 25 years. Halting that rise required a cultural change which was hard and could take time, Mr Balls said.

School heads, primary care trusts and social services departments were also crucial partners in helping to improve child wellbeing, he added. But ultimately parents and children needed to change their behaviour.

A campaign is being launched tomorrow to fight the decline in school meal uptake that followed moves to bring in healthier menus, spearheaded by celebrity chef Jamie OIiver. The aim is to get an extra 1 million pupils eating school meals a day.

"But I'm not going to legislate for what children can have in their packed lunches," he said.

"What we can do is offer support and legislate for areas [such as advertising] outside of parents' control."

Parents also need to strike a balance between being safe and letting children play outside, he said. The government could help by letting them know, for example, that road traffic accidents had decreased.

He inistsed there was still a role for government targets. 86% of schools now offer two hours of sport a week, up from 25% five years ago. The aim is for five hours a week by 2010.

But girls lagged behind meaning good school leadership was also vital to initiate activities such as pilates and trampolining which some schools had found boosted girls' participation.

"I'm an optimist. There are great opportunities for children in our society," he asid. "We can understand the pressures but open up opportunities. That's our mission," he said.