Children aged five and 11 are measured at school
One in three adults in the UK will be obese by 2012, researchers warn.
It comes as the latest government figures show no drop in the number of children who are obese, despite a raft of strategies to tackle the problem.
By 11, 33% of children are overweight or obese, data from the National Child Measurement scheme shows.
Writing in the Journal of Epidemiology and Community Health, UK researchers said 9,000 adults die early every year because of obesity-related illness.
Using data on 128,000 adults in the Health Survey for England, the team from University College London, calculated that 13m adults will be obese by the time London hosts the Olympic Games.
Almost half of them will be from low income and disadvantaged communities, widening the health gap between the richest and poorest, they said.
The government introduced the child measuring scheme in 2006 to monitor the impact of strategies to tackle obesity.
Initially uptake was low, but in 2007/08, 88% of children in reception (age four to five) and year six (age 10-11) were measured - equating to almost one million children.
In reception, 10% of boys and 9% of girls are obese, the figures show.
By year six this increases to 20% of boys and 17% of girls - figures that have not shifted since 2006/07.
Public health minister, Dawn Primarolo, said: "These figures show that there are still too many children who are overweight and obese - that's why we're supporting families to lead healthier lives.
"Change4Life will provide everyone with the information and support they need to improve their lives."
Dr David Haslam, a GP and clinical director of the National Obesity Forum, said prevention strategies alone would not help.
"We're still going to have a bunch of obese people, prevention is no good unless you also have weight management strategies."
Tam Fry, chair for the Child Growth Foundation, said he was unsurprised that the Department of Health's measures were failing to reverse the obesity trend.
"We had high hopes that there would have been a marked improvement after all the money that is being thrown at the problem but it seems that more radical measures will be needed to reduce obesity levels," he said.
Liberal Democrat health spokesman, Norman Lamb said it was "horrifying" that one in three children were overweight or obese by the time they leave primary school.
"The costs and impact of obesity, both for individuals and the health service are enormous.
"The NHS ultimately faces bankruptcy if we fail on this."