"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.