my sister's kinda picky about the games she'll let them play so i gotta kinda be careful. besides currently the only multiplayer game i have is world class baseball. my brother never sprung for a turbotap or anything so i only have what he has.
Luckily, Parasol Stars and Bomberman(s) are totally mom-friendly since they're cut. Plus, they're both fun as heck, so I think they will be a hit with the kids.
I strongly recommend Dungeon Explorer and Cadash, if mom approves, since they are a blast to play (especially DE).
Motoroader if fun, but I fear It might get frustrating if the kids aren't savvy drivers. I really enjoyed multi-player games, though, especially because you can upgrade your car.
Aeroblasters is a tough game, but it rules. But it is tough for little ones. IIRC, when you play co-op, you can bump each other and create a special weapon.