http://www.cfc-cafc.gc.ca/faq/transfer_cession_e.asp
Q. Can I borrow a firearm that is registered to someone else?
Yes, if you have a firearms licence that is valid for that class of firearm. When you borrow a firearm, borrow the registration certificate too so that you can provide proof that the firearm is registered if you need to.
If you do not have a valid firearms licence, or if your licence is not valid for the class of firearm you wish to borrow,
you may borrow the firearm only if you are under the direct and immediate supervision of a suitably licensed adult (aged 18 or older) and there are no court orders prohibiting you from possessing firearms or other weapons.
This was taken from the CFC site. What I read here is; your son is unlicensed but he can borrow one of your firearms as long as you have direct supervision over him and you are a licensed adult.