They have to make this decision based upon who's standards? ESRB ratings would make it easy, but is there more?
I can see and actually agree with not selling M rated games to kids; if mommy and daddy say it's ok for little Johnny to buy Doom 3, they need to be with him when he buys it. No problem.
As adults, we are free to make the decision what legal substances we pollute our minds and bodies with, and as a parent I hold the decision authority for what my kids will/ will not be exposed to. Without knowing more about this proposal, I would assume the bar will be set with ESRB ratings or some similar scheme and so would think that it helps me as a parent decide what my minor kids can and can't have.