Hockey helmets are a great choice for protection in SCA youth combat, but may require addition of an “aventail” — a flap hanging from the back of the helmet to protect the base of the skull and the back of the neck.
In this video, Master Hroudland Who Wanders demonstrates one approach to constructing such an “aventail” or “back flap” using a sheet of material cut from a used plastic barrel along with some common tools you might have in your garage.