Weight-loss programmes can help even very young children slim down, and it appears that acting early may improve the odds of success, according to two European studies.
Excessive weight in childhood often stays into adulthood, where it has been linked to heart disease, diabetes and other health problems.
In one study, which appeared in the Archives of Paediatrics & Adolescent Medicine, scientists in the Netherlands found that heavy three- to five-year-olds saw continued benefits from a weight-loss intervention at least several months after it ended.
A report from Sweden showed that overweight and obese children under ten were much more likely to have slower weight gain than adolescents getting similar behavioural treatments.
"What they are showing is a pretty consistent trend that if we were to intervene early, we could really have an effect on changing the trajectory of weight gain in children," said Elsie Taveras, a paediatrician at Harvard Medical School and Boston Children's Hospital, who co-wrote an editorial on the findings.
Dr Taveras said there is mounting evidence that paying attention to young kids may be a promising way to stem the global obesity epidemic.
In 2008, more than a third of US youths were either overweight or obese, according to the Centers for Disease Control and Prevention.
The numbers have also been on the rise in Europe, although they are lower than in the United States.
The Dutch researchers, led by Gianni Bocca of Beatrix Children's Hospital in Groningen, studied 75 heavy children who had been randomly assigned to either usual care or an intensive weight-loss programme.
The programme lasted four months and involved 25 sessions with dietary advice, exercise and, for the parents, behavioural counselling.
A year after the study began, children in the intervention group had gained 1.9kg on average, and those who got usual care had added another 3kg.
While that difference could have been due to chance, there was a statistically reliable difference in body mass index (BMI), a measure of height in relation to weight.
Children in the intervention group went down one unit in BMI, while the others saw no change.
"The magnitude of the effect, especially initially after the intervention, wasn't very large, but what needs to be taken into account was that these children were growing," Dr Taveras said.
"What these interventions are showing is that you can have an effect, and hopefully these interventions are changing the trajectory these children were headed towards."
She cautioned, though, that the Swedish findings, in a study led by Pernilla Danielsson of Karolinska Institutet in Stockholm, were based on observations instead of an experiment.
That means it's possible that the children between 14 and 16, who saw no or little effect of the behavioral treatment, could have been particularly tough cases.
Still, Dr Taveras said, there is good evidence that heavy children who start weight-loss programmes early have an easier time slimming down.
"I hope that in a few years there will be more examples of programmes that aren't just clinical that we can send families to," she said.