The supporting roles all feel truncated and a little underdeveloped. The kids should absolutely be the focus, but it felt like there was something missing. The starry cast were all great, but most roles amount to little more than cameos. I loved the Bruce Willis role and his performance -- my favorite of the adults.
I agree with most of your assessment except for this. I felt that when I was watching the children interacting with each other or when I was watching Frances McDormand and Bill Murray interacting with the children, I got lost in the movie. However, Edward Norton and Bruce Willis did not reach the bar set by the rest of the cast. That is not to say that Bruce Willis did not have good scenes. However, as the film wore on, the character's realness slipped away. This is a shame because Bruce Willis worked so hard to build the character in to something honest and sincere in the first and second act. Edward Norton had flashes of brilliance as well. But, they were just flashes and never really developed into anything substantial. As a result, both characters drew me out of the film to such an extent, especially towards the climax, that it hurt my enjoyment of it.
I also thought the film had problems with finding its tone towards the beginning - which was very jarring.
You get one scene that is played straight (and is really well done and beautiful) and then the next scene is campy (also fairly well done) and then the rest of the film is so unlike those two scenes (or maybe where those two scenes meet in the middle).
However, once the film
, I really enjoyed the performances, the beautiful cinematography and how the plot developed. I think it is a testament to just how good the film is that it was able to win me back after I turned hostile after the first 5-10 minutes.