This Saturday, a group of 11-12 year olds are going to build their own lean-to shelters in the woods and then sleep in them in 27 F temperature

Nothing! I had a 4H project for a couple of years, Outdoor Adventures. I taught the kids survival skills, every winter we would go winter camping, build a shelter, firewood gathering, no chainsaws, matches only to start a fire. Sometimes it got pretty chilly -15C. Couple of kids were the 4H minimum for age (9 years old). Nobody died, everyone had a blast!! It was one of the most popular projects in our club!