There were lots of restless kids at the showing I attended as well, with numerous walkouts during the second half. This felt a lot more like a sweet little independent film than a mass market family film.
A few observations (and huge spoilers):
Spoiler:
This movie didn't have the usual character arc that most Pixar movies use so prominently, even predictably. Our protagonist Remy begins the movie as a boldly confident and highly competent chef, and ends the movie the same way. He has occasional lapses of confidence or judgement, but these are nearly always addressed right away by his imaginary mentor. His circumstances change, but at the end, he seems to me very much the same rat he was at the outset. (Even his harsh lesson about how humans usually treat rats doesn't really seem to matter much to him, or to the plot.)
Our secondary protagonist, Linguini, bucks expectations even further. Has there ever been a more passive movie hero? He's practically a prop. He begins as a lovable loser with no cooking skills (nor any other talents), and there he remains. I guess he learns that he's fit to be a waiter (on skates even) but the movie makes no big deal about this. He's very much the same likeable shmoe at the end of the story, with modest (to say the least) ambitions. He gets the girl, through no effort of his own and on false pretenses. (I couldn't help but wonder if Colette keeps him around because he is so easy to control. Indeed, she could make him into an excellent bedroom partner just by pulling his hair in the right way.)
The biggest arc belongs to a minor character with only a handful of scenes, but that character's big moment of revelation, and his subsequent review/thesis statment, become the heart of the story.
None of this is meant as complaint, just somewhat surprised reaction to a movie that wasn't quite what I expected.