Having had three kids and living in an almost nordic country (Estonia) I can confirm that yes, indeed infants do sleep outside in winter temperatures. Mine did as well and they're fine and of regular health.
The trick with sleeping outside is that you have to make sure that they're warm and that there is no wind directly blowing at their face and there is blankets and stuff surrounding. In this case, breathing actually creates a zone of warmer air, so they don't breathe in the super-cold air all the time. The upside is that they get to sleep in fresh air and the parents get some free time. Win-win.
Regarding scool-age kids not being left left alone, I can't even imagine how this could possibly work. School for my eight year old is done by 12:45 - I work at least until 17:00, usually even a bit more, so does his mom. He comes home after school, warms up his meal (using a gas stove with an open flame - never had an accident or even a mishap with this btw) and on the days that he has swimming practice takes a bus to that. Trip from school to home is about 8km.
I'd actually kind of like to know, how do people manage work in the US, where I understand that this kind of behaviour is not allowed. If I were to pick him up after school and come home with him every day, it would mean that I could only have a half-time job maximum..