Rod said:
First thing that came to mind:
But well, since you're probably looking for something on the DS... I dunno, maybe waiting for Atlus' Devil Summoner? It's been just announced, though... =/
Dammit, I was going to suggest that.
But yeah, not available for the DS. Now, for the GBA there's the Demikids spinoffs -- which are, obviously, as the name implies, SMT aimed at kids. But still not as much at kids as Pokemon; you're still summoning demons, say. And if you play Demikids dark,
just about the entire game takes place in Hell. Atlus has an odd concept of how to aim things at kids.
Or, of course, you could always play the SNES Shin Megami Tenshi games. I'm not sure any of the SNES emulators for the DS will handle them properly, but they're not really aimed at kids, at least...
In terms of GBC games, there's Magi Nation. That's still kinda aimed at kids, but perhaps not quite so heavily... and the mechanics are a bit deeper. You might like it.
Digimon is all right as long as you can stand the fact that they put the word 'digi' in front of everything (seriously, everything.) Also, only the very first NDS game is worth playing. Since you can have multiple creatures out at once, the fights feel more interesting and less glorified rock-paper-scissors-ish. Someone should make a patch that removes every instance of the word 'digi' from the digimon games, it would actually make them much less cringe-inducing. It would probably also cut the filesize by, like, 50%.