Continuity mistake: In the first film, it is mentioned several times that Kevin is 8 years old. However, in this film it is stated that he is 10. When his parents are in the Miami airport security office, they say that he was left alone last Christmas. That would make him 9. Both films take place the same days, from about three days before Christmas until Christmas morning, so even if Kevin is born around Christmas time this is still a mistake.
Continuity mistake: The tiger bites the seat off the suitor's trousers, allowing the viewer to see his polka-heart boxers. When we see the tiger in the courtyard, he has a part of the same boxer shorts in his mouth. So if he bit off the seat of the trousers, shouldn't he have purple cloth in his mouth? (00:11:45)
Continuity mistake: When Adam Banks is playing in one of the games, he scores a goal and his teammates on the bench stand up and cheer when he scores. Problem is, Adam Banks is on the bench too.
Continuity mistake: In the scene where Gabriel Byrne is dancing around the fire with the travellers, he is wearing a large leather coat. After the police come and go, he's no longer wearing the coat. In the same scene, it shifts from night to day quite quickly, too quickly to be a sunrise.
Continuity mistake: As Jack Kelly rides the horse near the end of the "Santa Fe" sequence, his hat is waving behind him. When it cuts to a different angle the hat is on his head. Note: This was a specific detail put in by the director, symbolizing the boy's mental transition from New York to Santa Fe. However, it failed and is commonly seen as an editing mistake.
Revealing mistake: There is an obvious stunt double for Grandpa during the fight scenes.
Revealing mistake: During the ghost of Christmas present, Kermit is walking with tiny Tim on his shoulder and you can tell Kermit is walking on a spinning drum. Right before the camera pans away you can see Kermit's feet slide like he stopped walking but the road kept spinning. (00:55:00)
Factual error: The baby is expanded to approximately fifty times his height, width and girth but it's explicitly stated that he retains his orginal mass. This means he will have the same volume as one hundred and twenty five thousand babies of his original size, but will weigh the same as before he was enlarged! That child is going to weigh much less than the volume of air he displaces. He's going to float away.
Revealing mistake: When George Newton comes into the house and it is raining he has an umbrella in his hand. If you look outside his door underneath the balcony it's wet, but further down the path the ground is dry.
Continuity mistake: In some shots there is no steam coming from the steamboat.
Other mistake: When Tod is going outside to see a statue of himself, as he gets closer to the door he runs into it, but he actually jumps at the door.
Continuity mistake: As Hampton's family leaves town for Happy World Land, the car's odometer approaches 100,000 miles and, at this point, Wade grabs a camcorder with his right hand and starts videotaping the event. But in the next shot however he's steering the car with both hands - and still operating the camcorder somehow. (00:05:50)