Not withstanding the debate of a minor's "legal ownership," my oldest son "owns" a Glock 45 (not a fan of the plastic and couldn't tell you more, though I am coming around) and an AR-15. My middle son "owns" a 20 gauge and a 30-30, and wants a first generation SIG P220. My youngest son is 2 and "owns" a couple of orange plastic relvolvers and is required to treat them as functional firearms based upon his comprehension at his age.
My sons "own" their weapons though most were acquired by the auspices of my good fortune and desire for their happiness. And are theirs PROVIDED they abide the rules of safety which is the singular requirement of ownership in my household. I have never had reason to ever revoke, or even threaten to revoke, a weapon, as they each must show mastery of all safety rules before my charity sees fit to bestow upon them a weapon.
Other disciplinary issues are handled within the scope of the rule broken. Punishments, such as "grounding," deprive them of time to use the weapons, but "ownership" of the weapon never comes into issue. Breaches of firearm safety, however, are simply not tolerated and should one occur, swift and immediate revocation is the applicable punishment. Since they believe me to be a man of my word with respect to safety, I have, as yet, to invoke the penalty.
I support responsible "ownership" of firearms for my children without regard to the legal age of "majority," for many of the reasons stated by Bovice.