I would personally pick Final Fantasy Tactics Advance.

It is pretty much Final Fantasy Tactics stripped down for children. The story isn't anythign to serious, but it still has a degree of seriousness. I LOVE the battle/growth system, which has changed a little bit and the mission based gameplay made me fall in love. If it wasn't for this, I would have steered clear of Tactics. I can't say to much for the sequel cause I picked it up for five seconds, hated it, and returned it. I was judging a lot quicker than I should have, that being said.

I've heard Tactics Ogre is really good, same thing with Suikoden.