Health reporter, BBC News
The proportion of obese children in the UK is rising
Front-line NHS staff are unlikely to have an impact on tackling childhood obesity, say UK researchers.
GPs and practice nurses told a University of Bristol team there were limits on what they could do to solve what is effectively a social problem.
Time pressures, a lack of treatment options, and parental reluctance to address weight problems prevented them having any effect, said staff.
The government said no one group could solve obesity on its own.
In the UK, around 27% of children are now overweight.
Writing in the British Journal of General Practice, the researchers said there had been moves to involve primary care staff in spotting and treating overweight children.
This includes 2006 guidelines from both the Department of Health and the National Institute of Health and Clinical Excellence.
But in a series of in-depth interviews with GPs, practice nurses, school nurses and health visitors, the researchers found this view was not shared by those on the front line.
GPs and practice nurses said they rarely saw primary school-age children in the surgery and when they did there were often more pressing problems to deal with than their weight.
If they did bring up a child's weight, a lack of treatment options or follow-up services, meant there was little they could do to help, said doctors and nurses taking part in the study.
One school nurse said: "I've got a child that's going into care...I've got another child that's coming to me because he's hearing voices and they're telling him to do bad things.
"If you've got those sorts of things, you have to prioritise those...childhood obesity comes way down the list."
Doctors also said they felt it inappropriate to mention a child's weight unless their health problem was related to it.
Participants also said the causes of obesity - poor diet and lack of physical exercise - were outside their control.
Even those who thought primary care should be involved questioned how effective any intervention would be.
Study leader Dr Katrina Turner said the 30 staff members who took part in the study had not seen any of the guidelines and they were unlikely to have a "meaningful impact".
"It would appear that primary care can only play a limited role.
"We're talking about an obesity epidemic - the people who go to the GP are the tip of the iceberg."
"We need to look at the availability of healthy food, safe places to play, how often children have physical exercise in the curriculum."
A Department of Heath spokesman said childhood obesity is one of the biggest health challenges we face.
"There is no one group that can solve it on its own and we do not expect primary care professionals will treat and support all overweight and obese children.
"We are committed to supporting GPs and other healthcare professionals so they are equipped to raise the issue of weight with their patients, to provide advice and, where necessary, to refer people on to suitable services that will meet their needs."
Professor Alan Maryon-Davis, president of the UK Faculty of Public Health, said: "The problem is there simply aren't enough 'suitable services' to cope.
"Family-based approaches can be effective. But we need many more specially trained healthy eating and physical activity advisors if we're at all serious about helping the large numbers of very overweight children."