If you are worried about getting the right balance between freedom and protection for game playing children, there is some good advice to be found at InformativePost

Most of it is common sense but it is worth seeing it written down. Keep an eye on the games on the computer, and maybe even play them. It also reiterates that most effective forms of advice for parents worried about children and computers. Put the computer in the living room so you can see what they're doing.

As much as I would like to be able to remind my children that I am keeping an eye on their gaming by leaving the odd high score in the charts, few games seem to have these any more and I have a more realistic idea of my abilities.

On that note, I'm tempted to add that, if you do play the game yourself, to keep it quiet unless you do fairly well. Otherwise you might be challenged to a mulitplayer game!