You answered the question yourself; Disney is involved. How dark and mature do you expect any game in which the main character always runs around with Donald Duck or Goofy at his side to be?

There's some deeper ideas and concepts in the games that do get simplified, but the storytelling does tend to gloss over some of the darker realities revolving around the themes. Kingdom Hearts 2 dives into it a little bit more toward the end, but don't get your hopes up too much.

That all said, I enjoyed both games very much. Then again, I went in taking an obvious note of the dominant presence of Disney characters and the very obvious E rating. I got what I expected, and so I wasn't disappointed.