Young girls are far more likely to be fat than boys for they are over-pampered by their parents and do not get enough exercise, warn researchers.
By the age of seven, one in four girls is too heavy compared with just one in six boys, a study of British children found.
Its authors blamed mothers, warned that 'puppy fat' should not be ignored, and called on parents to act early.he Institute of Education analysed the weights of 11,000 children taking part in the Millennium Cohort Study - which is tracking youngsters born between 2000 and 2002.
Seven-year-olds who are only children are 25 per cent more likely to be overweight than those with one sibling and 30 per cent more likely to be overweight than those with two.
It is thought this is due to over-indulgent parents and a lack of playmates at home.
Youngsters with an overweight mother or father, or a mother who smokes, are also likely to be heavier.
At the age of seven, girls of average height - 4ft - were classed as overweight if they weighed more than 4st 3lb, and obese at 4st 12lb. Boys of 4ft were overweight at more than 4st 4.5lb and obese at more than 5st.
"Girls and only children are more likely to become overweight between the ages of five and seven. It is not clear whether the increased risk for girls is due to them being over-fed compared to boys, or because they are involved in less physical activity - perhaps due to the over-protectiveness of parents - or some combination of the two," the Daily Mail quoted Principal author Dr Alice Sullivan as saying.
"Similarly, we do not know whether only children are less active due to lack of siblings, or over-fed by indulgent parents.
"Either way, making parents aware of the increased risk to girls and only children may help to modify their behaviour," Sullivan added.