Legal advice is not available on this forum. You will get opinions, but these are not legal advice. Sounds like you acted responsibly in this regard. You might want to look at your terms of service to see if it might need an update to reflect the fact that minor children play the game an no improprieties will be allowed, resulting in instant termination. Then again, if you take on the responsibility you are assuming a liability, particularly in the event you FAIL to terminate upon notice. Two-edged sword!