Then the parents have to keep their kids on a tighter leash. When we get into this kinda scenario this becomes more of a house hold problem. Kids being rebels and such. Whether they got the game with a credit card via online or got it from another adult this then becomes a game of trust between parent and child. Like say if a kid wants to buy a fighting game like SSB. Some parents wouldn't get the game till they're a certain age like 9 or 10. Then with a game like CoD they wait till 12 or 13. It's basically like saying, "you're proven to me that you're mature enough to play this and I trust to not to do anything foolish like actually kill someone/something illegal."
This goes for language as well. For me, in my house, I basically can do or watch whatever I want as long as I keep respect towards others around me. Like I could swear words with friends but not older adults. There's a video I found about bad words that I found interesting and I'll put it in a spoiler.