The government will miss its target for halting the rise in obesity in children under 11 without clearer leadership from the top, the National Audit Office, Audit Commission and Healthcare Commission warn in a joint report today.

The target of stopping the rise by 2010 was set in 2004, but plans to tackle the growing numbers of overweight children as young as five through diet and exercise at school and home have hardly got off the starting blocks, the report makes clear.

The scale of the rise in childhood obesity is alarming. In 1997, 9.6% of children under 10 were obese. By 2003, that had risen to 13.7%. The cost of obesity to the NHS is about £1bn a year. On top of that are indirect costs to the economy of between £2.3bn and £2.6bn a year, which could rise by 2010 to £3.6bn a year.

The report points out that the issue involves "changing the behaviour of children and their parents, and attitudes in society generally". A number of initiatives are planned and some are under way, but there is little evidence yet to show whether programmes to improve children's diet and increase the amount of exercise they take will work well enough to meet the target. The government has published guidance on weighing and measuring children, but there are no clear figures yet about the extent of obesity in individual areas.

The report warns that organisations are unclear about their roles because they have not yet received proper guidance.

Anna Walker, chief executive of the Healthcare Commission, said: "If we are serious about tackling childhood obesity then all government agencies and organisations must work together more effectively. Those of us involved in inspection and assessment must ensure that this partnership working really takes place nationally and locally."