Plot hole: The parents meet and get married on the QE II and then we jump to the girls getting to camp 11 years and nine months later. We learn their 12th birthdays are on October 11, so at the time of the camp (which must be around July/August) they are 11 years and around 9 months old. They should only be 11, given it takes 9 months to grow a baby, but instead they're nearly 12.
Continuity mistake: When Dennis Quaid sees Elizabeth and falls in the pool, its broad daylight, but when she helps him and they're sitting down, its twilight and there are a lot of lights on, but when they see his fiancée they stand up and it's broad daylight again. (01:29:40)
Revealing mistake: When Meredith meets Nick and Elizabeth at the pool, Hallie comes up on her left and says, 'Hi, Mer.' Then Annie comes up on her right and says, 'How's it going?' Meredith shrieks as she looks from one girl to the other and you can tell that Annie is not really there, because Meredith is looking over her head rather than directly at her face, which she does with Hallie.
Continuity mistake: When Hallie and Annie are in the isolation cabin, you see the bucket that the water is dripping into from the leak in the roof, on a stack of books. After the wind blows all of Hallie's pictures off the wall they are sitting on the ground picking them up, Annie is seen picking up Hallie's little animal (Cuppie) right next to the bucket of water, which is now on the ground with no stack of books to be seen. (00:29:07)
Continuity mistake: When Annie and her friends are approaching the area where the fencing is taking place, all three girls are holding tennis rackets. The shot switches to the camp counselor and back to the girls. The African American girl is no longer holding a tennis racket. The shot goes back to the counselor and then to the girls again, where all three have a tennis racket again.
Continuity mistake: When Annie and Hallie are playing poker, Annie puts down a pound. In the very next shot, when Hallie puts down a £5 note, the pound is gone. There wasn't a big enough pile of stuff yet to hide it. (00:14:35)
Continuity mistake: When Hallie is posing as Annie and is going to her mother's house for the first time, a piece of her hair is obviously sticking out on the side of her ear (It's very noticeable). When she gets to the front, and the camera angle changes, her hair is all perfect without any hair sticking out.