I'm the author of the blog about the coats & car seats. We are a bit further south but we still can certainly have cold temps. I'll have to have my DH dig out his training manuals from his NSTC training...they have a little chart showing the time it takes to become affected by the different temperatures. Basically at -40*F, frostbite starts within 10 minutes of continuous exposure--and that's bare skin, outside, no attempt to warm. Walking outside, getting in the car, getting buckled, and getting covered, all while wearing some sort of coat and skin protection (hat, mittens, boots etc) is not going to cause frostbite. It might be uncomfortable but it's not going to create damage.
Googling shows very, very few reports of hypothermia in children--the ones it does show are those who get lost, or left in the car for extended periods of time. In fact it's hard to differentiate since it's all lumped together with the overwhelming numbers of hyperthermia.
In contrast, ejection from the vehicle is a well-documented danger. As I cite in my blog,
Quote:
A common question is "but are there cases of children actually being ejected from their car seat?" The answer to that is yes, there certainly are. In 2009, 76,309 people died in car crashes. Of those, 1538 were under the age of 16, and of these, 909 were fully or partially ejected.
And those are ONLY the deaths. The number of injuries are much, much higher than that.