I do not have any hatchlings in my outdoor enclosure, but I do winter Eastern box turtles and spotted turtles. Sounds like you in an area with a similar climate to me (Northeastern South Carolina) I added about a ten inch layer of leaves to the six inches of hay I already had there. I put the hay down early in the fall so that it begins composting. The composting produces heat. I also have a removable roof on my enclosure to hold in a little more heat. If I had hatchlings I would most likely bring them into a cool room in the house just to be on the safe side. Hope this is helpful.