Pretty darn cool for them Max was elated when Mickey Mouse and Donald Duck were out, and clapped and danced to the first few songs. He was over it by the reindeer song but I got him to stay until intermission (Let It Go is the last one before the break, it's out of sequence) by bribing him with popcorn and a new toy.
Overall, I enjoyed it because I enjoyed the movie. Max loved the parts he was really familiar with, so I think if your kid actually watches the movie (mine prefers TV shows), they will enjoy the show immensely.
My two absolutely loved it. I was shocked she stayed seated the entire time. She did sit on H's lap for most of it but that was because she couldn't see.