Mario & Luigi: Partners in Time is a good RPG, naughty naughty kids for losing it.
Children of Mana is basically a dungeon crawler, calling it an RPG is a little of a stretch, it's a great dungeon crawler and Talili and I are still playing it multiplayer (each person needs a cart though) and multiplayer it really is a blast.
FF3 I was thinking of getting but it sounds like I should avoid that, though in June I'll be import Pokemon Pearl from the US and that's enough Pokemon RPG to keep me going for a long while. And I've still yet to finish Zelda on the Wii so I've enough to keep me busy.
Personally I'd get Children of Mana if other people would also want to play it (single player I imagine it would get repetative), other than that cancels the kids pocket money and buy another copy of Mario/Luigi