If you (ahem... your kids) have a Nintendo DS (lite) then you MUST get an R4DS. It's a card that allows you to boot DS ROMs from a micro-SD card, which can hold 30+ games on it -- depending upon the size of the SD card and the size of the game.
Luckily I downloaded the ROMs for games I actually own, but there is definitely room for abuse here.
check out: www.r4ds.com and www.rom-freaks.net
enough said.