All the kittens in "The Nine Kittens of Christmas" have been adopted by people who were involved in making the movie.
All the original cast returned for this sequel...even Ambrose the cat.
Ambrose is played again by Trace the cat.
As with the original movie, there's at least one reference to Brandon Routh's prior role as Superman: during their conversation in the grocery store, Marilee calls Zachary a superhero for rescuing so many cats, and goes on to say that he's probably been called that before.
The kitten that was called Rudolph in this movie was actually named Calvin. The other eight kittens didn't have names yet during the filming of this movie.