Found these 3 sites that offer 100's of FREE games for the PC (which you can download onto your pc for later use), seems perfect for the kids to mess about over xmashttp://www.gametop.com/http://www.freegamepick.com/http://www.funpcgame.com/
I've downloaded 1 of the games so-far and it's virus free (checked with KIS2011) so all seems quite kosher with the sites!
Some of the games are chargeable but that's only a small number. The bulk of them are FREE.
Enjoy the free games!