I wouldn't say he expected any different; I think he just loathes the fact that these "kid's movies" are, as you called them, simple, or better yet, simplistic.

He thinks the movie does a disservice to kids by presenting what is, in his opinion, a distorted and sugar-coated representation of mental life and motivations.

Essentially, he thinks that a good movie would pass to viewers what Malick's Tree of Life does about the inner life of children (feelings of wonder, the need to act out for its own sake, the deception ones does for others and even oneself, etc) in a way that would appeal to kids.

(By the way, this is just what I understood from the review; I haven't seen Inside Out)