Originally conceived as a direct sequel to Jumanji. The visual effects supervisor on that film, Ken Ralston, was lined up to direct before Columbia abandoned the project in favor of adapting Zathura.
While the film was being made, Jonah Bobo (Danny) lost four teeth, so the filmmakers made 'flippers' or fake teeth that he wore, since the movie takes place in only a day.
In every Chris Van Allsburg book, there is a bull terrier named Fritz. Jon Favreau put Fritz in the movie - look for a Beanie Baby bull terrier behind Walter near the end of the movie.
The trivia items below may give away important plot points.
The numbers spun by Danny and Walter (respectively) are as follows: (5, 9+Move ahead 2 spaces), (4,8), (7,6+Move ahead 4 spaces), (6,8), (6,0 [walter get's ejected]), (8 - Move back 2 spaces, 9), (9 - Move back 1 space, 3 - Move back 3 spaces), (1 + Move ahead 9 spaces - Danny wins the game).