Almost one in 12 six-year-olds can now be classed as obese, according to the Health Development Agency.
The number of obese children in the UK is growing
It has called for parents to take action to improve the health of their children by monitoring their diets - and encouraging them to exercise.
Obese adults are at a higher risk of heart disease, cancer and diabetes, losing on average seven years of life.
Almost two-thirds of men and half of women are either overweight or obese according to the HDA's figures.
There are concerns that young children are eating too much fatty junk food, and adopting "couch potato" lifestyles.
Dame Yve Buckland, the chairman of the Health Development Agency, said: "Parents can make a huge impact on rising levels of childhood obesity.
"The good news is that the evidence shows parents can successfully treat their child's obesity by actively changing the whole family's approach to diet and physical activity.
"The myriad of child-focused food advertising is a real challenge, but parents can fight back - it's them paying at the checkout, not their children."
Professor Mike Kelly, the HDA's director of research and information, said: "Obesity is a health inequality issue - studies have shown that it is children from poorer backgrounds that are more likely to suffer weight problems.
"We live in an 'obesogenic' environment - a plethora of fast food outlets, reliance on cars and offers enticing us to eat larger portion sizes all contribute to the problem."
Health minister Melanie Johnson said that government had introduced initiatives - such as the National School Fruit Scheme and the Food in Schools Programme in an effort to improve matters.
She said: "We also want to see much more progress from industry to reduce added levels of salt, fat and sugar in processed foods."
The cost to the NHS and economy of obesity in the UK is estimated at £2.6 billion a year.