As you know, all games are not made to be played by children. You should know what games you kid likes and who they are playing with if the game is an online multiplayer game. You should know about the Entertainment Software Rating Board or the ESRB. Learn more here
Understanding the ESRB allows you to control what your kids are playing. Head over to Parentaltools.org to have an even better understanding of different types of games your kids may play.