The coldest I recall from living in Bismarck, ND was -49°F. It reminded me of Jack London's short story, To Build a Fire. In the story the main character's spit would freeze with a snap before it hit the ground so he knew that it was at least 50 below. Well, I figured 49 below was close enough so I tried it. It didn't freeze. Maybe he was taller than me.
My kids went outside and played. My Norwegian in-laws always said, "There's no such thing as bad weather—just bad clothing."