Canadian researchers have found children who attend daycare are more likely to become overweight or obese than children cared for by their parents.
The study, which has been published in the Journal of Paediatrics, followed about 1600 families in Quebec.
Researchers at the University of Montreal found that children who attended daycare or were cared for by a member of their extended family between the ages of 18 months and four years were about 50% more likely to become obese by the time they were 10.
The researchers say they don't know what causes the difference but have ruled out the usual risk factors such as socio-economic status, whether the child was breast-fed or whether their mother was obese.
They say parents shouldn't pull their children out of daycare but should make sure they are getting the right mix of food and exercise both at home and in daycare.
A New Zealand child obesity expert says parents should not be alarmed by the research.
The Director of the Liggins Institute at Auckland University, Professor Wayne Cutfield, says the link could be unique to Canada because several American studies have shown no relationship between obesity and daycare.
Professor Cutfield says most New Zealand kindergartens and preschools have healthy eating policies.
But he says parents should be vigilant about their children's diet and exercise as there is a strong link between childhood obesity and weight problems in later life.