steam
I have been collecting games in my Steam account for a while (I can't resist those 75%-off sales!)
Now my son wants to play a few of the milder games, but I don't want him to have access to my FPS games.
Ideally, I'd create a new Steam account for him and move the non-violent games to his account.
Is this possible?
Yes, he would have to have his own steam account and buy the game separately if you want to track achievements independently. A single Steam account is intended to be used by a single person only, so it is not surprising this is how it works.
If you go in-game and do shift+tab, you get that odd overlay menu. in the friends pop-out there is your name, and a settings symbol next to it.
click it and you get a "friends light settings" menu
go to the Notification tab and uncheck everything
Best Answer
Unfortunately, Valve will not let you transfer games to a different account, unless they are gift purchases. As suggested in SqlACID's answer, you can create a separate account login for your son that still uses your Steam account login and password.
If you have Windows Vista, Windows 7 or Mac OSX you can additionally setup parental controls to disallow the launching of games that you don't want him to play.
If you want him to be able to launch games directly from Steam, I would suggest creating a new game category specifically for him and then add all the games you want him to have access to. To do this, right click a game and select Set Category..., then add a name. You can then select that category at the top of the games list. Here's a rudimentary example: