I play GTA Online with my son. I'll admit, Mum isn't impressed, but we have a ball on-line.
At first it was NO ON-LINE play for him as I sat beside him & watched him have a go off-line. I think those first few days / weeks were more fun for me watching him learn the controls, get hysterical over game play & generally learn every facet of the game.
Then it was time for on-line... We started off on invite only sessions (strictly). I was surprised how aged my son was playing the game. We did this for another week or so & I had to explain a few things about life. He's "just" pre-teen. I knew he'd find them eventually, so I took him to Heff's mansion & to the strip club. He immediately turned around, red faced, calling me for everything. Again, I knew he'd see it when I wasn't around, so I got on the billy in my high end apartment. This disgusted him. I asked him about the sex & drugs in the game & he replied with "I just avoid it Dad".
We started on free roam "sheepishly". We avoided people at first, heading straight out into the desert. he'd listen to others, while on mute, & often say that "these people carry on like d*ckheads" or "this bloke's a fruitloop". I started to feel more comfortable with him playing an on-line game.
He now goes on free roam on his own. in all honesty, I did think he would revert to be one of the pain in the butt squeakers, but to my surprise, he actually has a good head on his shoulders. I have often walked in on him & he is helping a lower level player (he's about 180 now) who was copping grief from some dirtbag or he's doing Rooftop & explaining what to do & how to do it with people on single figure ranks, helping them to rank up. He'll look for single figure players, not to hunt, but will give them his fully optioned Zentorno, his Monster Truck or one of his planes or a Buzzard, just so they can have a go with higher level equipment or he might drop a high end gun so they can protect themselves a bit better.
I can't speak for everyone & my opinion is mine alone, but if done right, I can't see any issues with GTA for younger players... the important words here... "IF DONE RIGHT"...!
I guess I have 2014's version of quality time with your kids.
BTW - Being closer to 50 than to 40, the little sh*t flogs the crap out of me if we "get serious" so it's good to have back-up with quick reflexes...!