If you are downhilling, you should have a full face helmet, as well as a neck brace. This is just my opinion of course. I bought my kids the Leatt Comp in the US. For whatever stupid reason, they're $200 more in Canada. I bought this after my son piledrove his head into a rock, and crushed his helmet. Fortunately it was just a mild concussion, and could have been a lot worse.
Here is a good article on them.
http://www.pinkbike.com/news/Leatt-n...view-2009.html