Research by the Institute of Child Health at University College, London nearly a quarter of all children are overweight or obese by the age of three.
Nearly a fifth of toddlers - 18 per cent - are heavier than they should be and 5 per cent are clinically obese.
The figures, based on the height and weight of 14,000 three-year- olds, comes as politicians and education authorities try to tackle youngsters' poor diets and lack of exercise.
The research, which is based on data from The Millennium Cohort Study - which is tracking children born in the UK between 2000 and 2002 - also found that those from poorer areas were more likely to be over eight or obese than those from better off backgrounds.
Among ethnic groups, Indian toddlers were the fittest, with only 9 per cent being overweight or obese.
Black Caribbean children were the least fit, with a third being overweight, compared to 23 per cent of white children.
Carol Dezateux, Professor of Paediatric Epidemiology at the Institute of Child Health, said: "The concerns were already there, but this confirms that messages to parents of very young children about diet and exercise need to be re-enforced.
"The message is that weight problems don't just start at school age - it starts earlier."
I wonder if the fact that most beverages are loaded with corn syrup and than fast food is a staple for most families has anything to do with these stats?