Tests to see if children aged four and 10 are overweight are being introduced in schools.
Children aged four and 10 are to be tested
The Department of Health has opted to go ahead with the tests, despite opponents saying it could lead to overweight children being bullied.
Pupils in England will be weighed and measured as they start primary school and again before they leave.
The results will be given to parents and local health chiefs, but overweight pupils will not be offered extra help.
The government said the aim is to give it and primary care trusts, which run community NHS health services at a local level, a better idea of which geographical areas have a childhood obesity problem.
According to figures published in the Daily Mail, a girl aged four of average height (3ft 3in, 99cm) is considered overweight at 2st 11lb (17.7kg). For four-year-old boys of average height (3ft 4in, 101.6cm), that figure is 2st 12lb (18.1kg).
At 10, a girl of average height (4ft 6in, 137.1cm) is considered overweight at 6st 11lb (43.1kg), and a boy of average height (4ft 7in, 139.7cm) overweight at 6st 7lb (41.3kg).
From next year, parents of any obese four or 10 year olds can expect a letter telling them their child faces long-term health damage unless they lose weight.
But parents will be given the right to refuse permission for the child to be tested and to ask not to be sent the results.
Guidance issued by the government to NHS trusts says the weight checks should be done wearing "light clothes" and nurses are urged to be sensitive to the risk of bullying.
A Department of Health spokeswoman said: "We feel this is a real chance for parents to play a more active role and to be aware of the health risks to their children of being obese.
"Weighing and measuring in schools isn't a new public approach. It was around decades ago. It is about helping us and primary care trusts get a better idea of what is going on.
"We are facing an obesity timebomb and need to sort this out and this is one of the measures we are taking forward."
Obesity campaigners have welcomed the move.
Dr David Haslam, clinical director of the National Obesity Forum, said: "I think it is a good thing as weighing and measuring does increase parental awareness."
Tam Fry, of the Child Growth Foundation, welcomed the move, saying it was about giving people the facts.
He added: "Parents are very ignorant about what a healthy weight is."
But critics have accused the government of being over-protective.
Margaret Morrissey, of the National Confederation of Parent Teacher Associations, told the Daily Mail: "It appears to be more of the nanny state and I don't think it is going to be terrible effective."
And Shadow Health Secretary Andrew Lansley said it was right to focus on the risk of childhood obesity.
But he added: "The problem is that at the moment government officials won't raise this with parents for fear of stigmatisation and the government have no idea what subsequent measures are most likely to be effective."