Visible crew/equipment: When the Elves fly off the roof with Charlie, a wire aiding in their takeoff is visible under one of them.
Continuity mistake: When Scott Calvin hears something on the roof and he goes outside, he sees Santa on the roof. He calls to Santa, "hey you", and Santa turns around and slips. As he's sliding down the roof, and falls you can see where Santa slid on the roof, because there is a line of no snow, in the next scene, like five seconds later, there is snow where Santa slid.
Continuity mistake: When Scott is talking to Charlie in the Zoo,we can see a polar bear swimming around in the background. One minute it is just behind Charlie and the next it is behind Scott - there's no time between shots for it to have swam across.
Audio problem: Outside the Miller's house the detective who was interrogating Scott is now shouting at the house with a bullhorn. When the detective lowers the bullhorn, his voice sounds like it is still being amplified.
Continuity mistake: On Christmas Eve, Scott runs out of the house to check the roof after he and Charlie hear a ruckus. Right as Scott sees Santa and yells "Hey You!", take a good look at the roof and the snow patterns just to the left of where Santa is and where he slips. Water and "wet" snow melt patterns also indicate an icy and probably a slippery surface. A few minutes later in the movie when Charlie and Scott ascend the magic ladder to find Santa's reindeer, the roof setting and snow patterns that were to the left of where Santa was originally standing are now completely different (and a flat, non slippery surface, no wet patterns), indicating a safer stage set.
Revealing mistake: When the elves are tying up the police officer at the station, they do so in a really quick manner. The film here is obviously sped up. You can tell this by the fact that the children playing the elves are breathing really fast.
Audio problem: When the cops stop the random Santa on the street thinking that he's Calvin, he says, "It's not even my suit! It's a rental!" But his lips are completely out of sync.
Revealing mistake: When the original Santa falls off the roof, the path he slides is already visible before he falls, especially in the point of view shot.
Visible crew/equipment: Near the beginning right when we see Charlie in the back of the car, the camera shadow creeps onto the vehicle as its moving.
Audio problem: When the elf special forces are about to take off and the female elf does a somersault, the sound that is created when they touch their wrist console can be heard over the sounds of the jet pack take off sounds. No one is even touching their wrists during the scene. (01:19:27)
Other mistake: A Federal Express driver delivers hundreds of boxes to Scott Calvin. They contain the names of all the children in the world. Scott opens a box and picks up the top page and begins reading the names. The second page in the box is identical.
Continuity mistake: After Santa falls in Scott's garden, before he vanishes he has some snow on the suit, but a few moments later the snow is gone.
Continuity mistake: In the first house visited by Scott as Santa, the amount of snow on the top of the chimney changes from shot to shot.
Chosen answer: Even though Charlie did not want to stay with his Dad for Christmas Eve, he did want to stay at home with a family member, fragmented as it was. Eating Christmas Eve dinner at a Denny's restaurant was not his idea of a Christmas dinner at home with family.