What should I do about my 6yr old kid playing GTAV while he's at his 5yr old cousin's house?

My 6 year old confessed to me this morning that while he was over his cousin's house yesterday (who is also 5 years old), they played Grand Theft Auto. I was not aware of what they were doing at his cousin's house but this is the second time I told my wife and my 6 year old kid that I do NOT want him playing that game. Look, I'm not that kind of parent. I get it. Video games are cool. I still play video games. I grew up on video games. I have a PS3 and I own GTAV but I don't let my kid play it or even see me playing it.....because it's NOT FOR HIS AGE.I was kind of annoyed that I had to have this conversation twice because this is the second time that he came home and told me that he played GTAV. My kid doesn't know how to lie and he always tells me the truth, so I know that he definitely did play that game. He told me that they were stealing cars and running over people and shooting police. This is not what I want my kid playing when he goes over his cousin's house. I told my wife this but the cousin's father is her brother (my brother-in-law) and she doesn't see what the big deal is, although she recognizes that this particular game is pretty violent and not for a kid as young as 6. Her reply was, "OK, he played it. So what?"If he wants to give his kid a PS3 at 5 years old and let him play GTAV, that's up to him but I don't want my kid playing that game when he comes over. When I went to pick up my kid, it took 20 minutes for my brother-in-law to answer the door because he was sleeping. So the only adult in the house at the time was fast asleep in the bedroom while my kid and his cousin were playing GTAV in the play room. I didn't send him over there to play video games for a couple of hours while his uncle took a nap.Am I out of line if I ask my wife to talk to her brother about this? Am I out of line if I talk to him myself? Should I talk to him about this or am I making a big deal out of nothing? The way I feel now is that I can't trust my brother-in-law to act responsibly when he's supposed to be watching the kids, and so I feel like I don't want to send my kid over there anymore. At the same time, I don't want to punish my kid and prevent him from hanging out with his cousin/best friend. Your advice is greatly appreciated. via /r/Parenting https://ift.tt/2GXlrv8