Stick with the tried-and-true.
Don't send Junior out into the cold, cold world without the protection he needs. The Burton Boys' Fray Jacket will keep him warm with a DRYRIDE shell and thermacore insulation. Burton's Room-To-Grow System ensures that you won't have to get him a new jacket right away because he just refuses to stop growing. The other solution would be to stuff him full of coffee and cigarettes, but that's not proven to work.