My wife and I played CoH in its early years and my son was not even a year old. Now that it is back, he is now 12 and my daughter is 10. We let them play on their own accounts, but only if me or the wife are also on. We have a regular family super hero night as a team of four savings citizens and beating up bad guys, but only within their normal allotted screen time (which annoys my son because he has a serious case of altitis). We even set up a discord since the computers are in different rooms. They are having an insane amount of fun and it spurs a lot of conversation outside of game.
I believe that with some controls in place and the present eye of a responsible parent, allowing your kids to play CoH can be a fantastic family event.