Continuity: There's a scene in one of the camp cabins where the two girls are talking. It cuts away from one girl, and she has an ice cream cone in her hand, then cuts back and it's gone. This keeps happening.
Great sites
Mistakes
When the girls leave camp they wave good-bye to each other. If you look closely it is obvious that one of the girls (the one in the distance waving) is a double who does not look like Susan/ Sharon at all. See more...
Trivia
Hayley Mills mom accidentally mistook Hayley Mills stunt double for Hayley. Hayley's mom tapped the double on her head and said "Hayley come on." See more...
The Parent Trap mistakes
Continuity: The dad drives "Susan" home from the airport. After he touches her face, he puts his hand down next to him, but when it cuts, his hand is on the steering wheel.
Revealing: When in Boston, while walking through the park, Susan and her mother are obviously walking on a treadmill because the park background is moving way to fast for their walking speed.
The Parent Trap trivia
Hayley Mills mom accidentally mistook Hayley Mills stunt double for Hayley. Hayley's mom tapped the double on her head and said "Hayley come on."
Hayley Mills had one stunt double that can be seen in the movie when one of the girls has her back to the camera or when Hayley is doing something she can't do by herself. The stunt double girl received a Duckster award for the best unseen performance by an actress - only three have ever been awarded.
For the scene when the camp girls are following the twins to the cabin Miss Inch was putting them in, the director wanted the girls to march like soldiers. The girls could not march very well, so he just decided to leave it as it was. The whistling the girls do is not the girls' whistling--its a recording of the march from Bridge on the River Kwai.