The children of wealthier parents, particularly those with working mothers, are more likely to be obese or overweight, a study says.
The study followed children to the age of three
Researchers at the Institute of Child Health in London followed 13,000 children to the age of three.
They found for every 10 hours worked the risk of being overweight rose once household income topped £11,000, the International Journal of Obesity said.
Experts said it was a "wake-up call" for the middle classes.
Some 23% of the children in the study were overweight or obese by the age of three.
But the researchers found a link between the risk of obesity and the amount of income earned.
Those earning £22,000 to £33,000 were 10% more likely to be overweight per 10 hours worked than households earning under £11,000.
While those earning over £33,000 were 15% more likely.
However, the researchers also noted that among the working mothers group - 7,500 in total - the risk was 13% and 19% greater.
The researchers said: "Long hours of maternal employment, rather than lack of money, may impede young children's access to healthy foods and physical activity.
"For example, parental time constraints could increase a child's consumption of snack foods and / or increase television use."
They said working mothers were also less likely to breastfeed for the recommended amount of time.
And those with higher incomes were more likely to have demanding jobs.
But the researchers also stressed the need for high-earning families with just one parent working to consider their behaviour.
They said those who earned more were more likely to be able to afford convenience food which could be contributing to the increased risk.
It comes as the proportion of working mothers has increased in recent decades. In the last 25 years the number of stay-at-home mothers has fallen from nearly 55% to just over 21%.
Dr Susan Jebb, head of nutrition and health at the Medical Research Council, said: "This is a wake-up call for middle-class families.
"Obesity is something that affects middle-class families as well, and that's important because many people take it to be an issue which only affects low income groups and it is absolutely not the case."