"The babies who nap in sub-zero temperatures."

"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."
"When the temperature drops to -15C (5F) we always cover the prams with blankets," says head teacher Brittmarie Carlzon.
Oh! Sub-zero centigrade. It's not that cold!

"Babies clearly slept longer outdoors than indoors," says Marjo Tourula. While indoor naps lasted between one and two hours, outdoor naps lasted from 1.5 to three hours.

"Probably the restriction of movements by clothing could increase the length of sleep, and a cold environment makes swaddling possible without overheating," she says.