More than 1.6 million children who started secondary school in the past decade were overweight or obese, new calculations show.
Between the 2006/07 and 2014/15 school years 1,654,894 children in England started Year 7 with an unhealthy weight, according to research from Cancer Research UK.
The charity added that obese children were about five times more likely to become obese adults, while it was found there is an apparent "weight gap" between the poorest and wealthiest primary-school aged boys. The report found 60% of the most deprived boys aged 5-11 are predicted to become overweight or obese by 2020, compared with 16% from the most affluent group of boys.
In contrast it was found about one in five girls is predicted to be obese or overweight by 2020 and there was no difference between the richest and poorest girls.
The charity said the findings show the Government must press ahead with their plans for a sugar tax on soft drinks, but that more work needed to be done. In particular the charity said there needed to be a ban on junk food advertising during children's TV programmes.
"From a young age, children are developing a taste for high sugar, salt and fatty foods that is difficult to break once established and as a nation, we all have a responsibility to help shape children's diets," said Robin Ireland, chief executive at Health Equalities Group.
"Sugary drink consumption levels tend to be highest among the most disadvantaged children who are hit hardest by obesity and tooth decay. The health gains from the soft drinks industry levy will be biggest for our most deprived children."
Professor Russell Viner of the Royal College of Paediatrics and Child Health said: "Obesity blights a childhood and damages adult life, raising the risk of serious complications such as type 2 diabetes and breathing problems - conditions we are seeing much earlier in childhood."
"We need to make healthier food the easier, cheaper choice by introducing advertising restrictions before the 9pm watershed, and testing the impact taxation has on foods high in salt, sugar and fat."
A spokesman for the Department of Health said: "UK restrictions on advertising are already some of the toughest in the world and we have been clear that we expect the food industry to take strong steps to make their food healthier. Our plan is the start of a conversation and we haven't ruled out further measures if we do not see the progress we need."