As others have said, games are not subject to the rules about buying for those under age. It's defined as a moral issue, and all GAME group employees are taught as such.
That said, everyone in any store I've worked in tries to make sure all buyers are aware of the content. It's hard not to give up though, as 9 times out of 10 the parent will buy the damn game anyway.
Please don't blame GAME for "milking" parents, they're a games retail company. Their real focus is sales, same as if you were in a phone shop or something, but most do agree that 7 year olds shouldn't be playing CODBLOPS or RDR.
We vigorously ID, and always mention the Age restictions to the adult. As I said, 9/10 times the adult doesn't care. We can't do much about that apathy. If we refuse the sale, the kid will just pester power the adult into HMV/Gamestation/supermarkets/indies.