Children placed in daycare are 50 per cent more likely to become obese than those who stay at home, according to international research.
The study, by researchers at the University of Montreal and the CHU Sainte-Justine Hospital Research Centre, also found children were more likely to face weight problems if they were in the care of relatives rather than parental care.
It found no reason why the difference should exist.
"This difference cannot be explained by known risk factors such as socioeconomic status of the parents, breastfeeding, body mass index of the mother, or employment status of the mother," said study leader Dr Marie-Claude Geoffroy of the University of Montreal.
The research, based on 1649 families in Quebec, was published this month in the Journal of Pediatrics.
But New Zealand childcare centres said they were often the ones to educate parents on being healthy.
The findings were "full of rubbish", said Flrorrin Keni, centre manager at Auckland's Southern Cross Preschool.
"It's definitely not the case in our centre - we're the ones educating the parents on healthy eating, exercising, healthcare," she said.
The centre provided morning and afternoon teas for their children, which included fruit and water.
Children brought their own lunch, and two years ago staff ran a healthy eating programme to educate parents because they were often giving their children fast food, pies and noodles.
Sam Gordon, manager of Wellington's Bowen Early Childhood Education Centre, said it had a chef who provided one red and one white meat and vegetarian options.
"We also have fruit with every meal," she said.
She said a lot of parents had to work and they needed to know their children were going to be looked after properly.
Dr Sylvana Cote, who co-directed the study, told the Mail Online that while the reasons for the difference in weight was not yet known, unhealthy meals and a lack of exercise could play a part.
"Parents don't have to worry; however, I suggest to parents they ensure their children eat well and get enough physical activity, whether at home or at daycare."
The researchers said daycare centres had the potential to reduce weight problems in children through the promotion of physical activity and healthy eating.
Study too simplistic, says mum
Lower Hutt mother-of-two Liz Martin's 2-year-old son Toby has been going to daycare for the last year.
She put "no stock" in the Canadian research at all.
"I know that my child goes to childcare and he eats better there than if he was at home with me."
A chef provided Toby's childcare centre with meals that provided "awesome variety", Ms Martin said.
"And he sits around in a socialised environment and watches others eat vegetables and fruit that I wouldn't be serving to him and he will eat it more than if I was at home trying to encourage him to eat it."
But she said not all childcare centres were the same. "His childcare is a really good childcare and they offer really good food and a good amount of food."
Ms Martin said one reason why children in childcare might face weight problems was because of stressed parents trying to cook something easy for their children.
"I find [the survey] a bit too simplistic."