We all know that Scandinavian kids sleep outside in their prams all winter long, wrapped in wool Onesies and down comforters, and that they're the healthiest, happiest, best-sleeping babies in any hemisphere. All that fresh air.
We also know that the concept of parking your kid out in the snow for hours at a time freaks foreigners right the hell out. [And actually got a Danish mom arrested in New York City once back in the day. Ooh brother, I remember that tabloid frenzy. If they didn't all think they were right, and the Euros are crazy, New Yorkers should've been thoroughly embarrassed over that one.
Anyway, don't worry, the BBC is ON it.
The key is wool against the skin, plus all the other stuff. And the optimum napping temperature is -5 degrees, but -20 or -30 works, too. Try it at home! But not in the streets, because you'll still totally get sent to jail.