There is an interview with both Maurice Sendak and Spike Jonze on HBO on demand. They flat out tell you it is not a kids' movie, but a movie about being a kid...haven't seen it yet myself.

i'm 24 and went with my husband to see it an i loved it. i can't imagine taking kids to see it, most would probably get bored. but i thought it was beautiful to look at, and i loved the story. i thought it really captured childhood, and how scary and amazing and frustrating it could be.