Nowadays most day-care centres in Sweden put children outside to rest. It's common to see rows of prams lined up in the snow at nap-time, with youngsters fast asleep inside.
"Daytime temperatures this winter in Stockholm have regularly dropped to -5C (23F) but it's still common to see children left outside by their parents for a sleep in the pram. Wander through the snowy city and you'll see buggies lined up outside coffee shops while parents sip on lattes inside. And if you are visiting friends and your child needs a nap, you may be offered the garden or balcony instead of a bedroom. 'I think it's good for them to be in the fresh air as soon as possible,' says Lisa Mardon, a mother-of-three from Stockholm, who works for a food distribution company."
BBC News - The babies who nap in sub-zero temperatures.