Do you hate your kids or what? Why didn't you bought them something of good quality, like Raving Rabbids? :P
Worst game I have played (I don't buy bad games) would be... well, would be a long list. Games like Big Rigs, Superman 64 are obvious in most lists.
A very crappy game I played was this Nintendo 64 game... Night Creatures or something like that. It was a port from a PSOne game where you dwelled on darkness-filled streets, killing and chopping monsters. A friend of the time thought it was a good idea to rent this game, because he loved it on the PS. After some minutes, I was like "dude... this sucks cack. Why the "&$%$@ I have to press "up" to move in ANY direction? The controller has a 3d stick you know... Let me give you some doses of Zelda, Perfect Dark and Banjo. That way you'll know what's good".