When you get sick of Nick Jr. and All That is the Marvel of Pixar and Disney, try these:
and My Neighbor Totoro.
Ponyo was the boys' first theater movie, and they were totally caught up in it, despite the somewhat odd little plot and characters. We recently rented Totoro, and they loved it just as much. The animation is old school, but gorgeous. The backgrounds are masterful; the imaginary characters are weird and just scary enough to keep the pre-schoolers on their toes; and the human characters have real life problems and flaws.
Both films were made by Hayao Miyazaki, who also makes more grown up animated film like Spirited Away (Oscar for Best Animated Feature, 2002) and Howl's Moving Castle. I'm looking forward to watching those with the boys in a few years. Disney is involved in the US versions. They have the rights to distribution or something, but they didn't mess with anything, so they're all original, except for the English dubbing.
PS: Voice of the mom in Ponyo = Tina Fey. How's that for cred?
I'm all for a good Toy Story or Nemo, don't get me wrong. But these 2 films are on a different scale of awesome. Check them out.