@BrianK

I feel few PSN games like Magic Ball, Super Ruba Dub and PuzzleFighter should be enough.

The Wii is cute and small and would IMO be a perfect with a small SDTV in a kid's bedroom. A nice control system. The Wii has so many cute cartoony games available for it, a nice fit for 6 year olds and up (I won't buy one without being asked for one, as I prefer kids to play with dolls, car models, LEGO, board games and such at home). For boys 11 and upwards maybe a PS2 instead, it's cheap and there are lots of cheap games, it can be handled without too much care.

Maybe I would even get a second hand Snes instead (sturdy cartridges!), Super Mario World is still a lot of fun (but I understand they may want something other kids play on as well).