Deliberate mistake: When bars are placed on Harry's windows, so he does not escape, it is apparent that his windows have complete leaded panes of glass. Yet when Harry is being rescued, Ron and Harry speak with each other, even in low voices, through his visibly closed windows. (00:08:00 - 00:09:00)
Deliberate mistake: At the end of the film, Gaston shoots the Beast with an arrow and pushes the Beast out the window. When the Beast lands on the edge of the castle rooftop, the arrow has disappeared. Even if part of the arrow has broken off, a piece of it would still be in his back. [This, like many other incidents in the film, is a longtime Disney animated tradition. The company seems to believe that violence is less unpleasant if all evidence of it disappears quickly. This is why so many cuts seem to disappear or become less serious. The arrow vanishing is just another example.] (01:16:55)
Deliberate mistake: When Lex tests the crystal fragment, it knocks out all the power on the airplane Lois is flying in, yet the flight attendant's amplified voice can still be heard over the speakers. (00:30:40)
Deliberate mistake: At the end just before the president is killed he fixes his tie, but it keeps on getting fixed to messed, to fixed, etc. Deliberate homage to "A Few Good Men", but worth looking for nonetheless. (00:28:15)
Deliberate mistake: When Sarah, et al are surrounded by the Goblins in Goblin City, the first cannon fires causing an explosion in front of some buildings, one of which has a hanging sign with scissors on it. Later, after the squatty Goblin says, "Hey! I just fired you!" another cannon fires causing an explosion, and the very same shot is shown, only the first one was flipped. (01:20:15 - 01:25:35)
Deliberate mistake: Charlie's room has a hole big enough for him to climb out of in the ceiling. I know it is to show just how poor the family is, but we see he has only a thin wool blanket for warmth. He would have frozen to death in his sleep during winter by now.
Deliberate mistake: When Alice jumps on the dog and they start running, her dress and her hand-band suddenly changed side. Probably they mirrored the image, and instead of going left as directed, it felt more accurate to go right.
Deliberate mistake: In the end of the NASCAR race, Tripp and Gordon get into a crash making Gordon spin, but he somehow is still able to come in second place even though every other racer was right on his back when he spun. He wouldn't have been able to regain that much speed in that short amount of time.
Deliberate mistake: Main headlines in newspapers appear translated for each country for the kids to understand it, but the rest of the news appear in English, despite the movie taking place in Paris. Also, most signs -such as the poisons in the window shop- have labels written in English.
Suggested correction: By that logic, it's a mistake that the characters speak English. It's an American movie set in France, and like you said, it's a kids' movie. Everything is in English for simplicity's sake.
Deliberate mistake: The Fremen wear "stillsuits" to conserve their water, yet leave their heads completely uncovered. This would result in quite a bit of water loss through perspiration. (In the book, they wore hoods, masks and nose filters, leaving only the eyes uncovered, but it wouldn't work in a movie to have all the actor's faces obscured!).
Deliberate mistake: The balloon llama the chipmunk makes has legs which are completely detached. The pairs of legs should be twisted together. Without this, it looks like the balloon has 6 different ends.
Deliberate mistake: Old Weird Harold's pants fall down twice in the film. His boxers are different colors each time; once they're red, the other time they're blue. The director admits to this deliberate mistake in the commentary, siting his interest in seeing if people will notice.
Deliberate mistake: Loch Ness is portrayed as a clear lake, as shown in the underwater scene. In real life, Loch Ness is so murky there is only six feet of visibility. Obviously deliberately done for the sake of the storyline.
Deliberate mistake: As Nancy and her Mum are leaving Rod's funeral, you can see the shot of them leaving the funeral has been sped up. Watch the Volvo "jerk" as it pulls away as the speed is rapidly increased.
Deliberate mistake: They keep using the same footage of Bela Lugosi walking in the cemetery, even the cars driving by out on the road are the same. (00:53:00)
Deliberate mistake: At the beginning, the carolers are on the porch singing. The camera never pans, so this means that the carolers are facing away from the house (towards Gate) - seems rather odd. The only reasons for this would have been to make the clean camera move through the crowd and up the house.
Deliberate mistake: After Ashley gets covered in mud, for the next five minutes or so of the movie the amount of mud on her constantly changes between shots, especially on the back of her head.
Deliberate mistake: During the dance number in the Dead Bar, the blue pirate has a sword stuck through him with the handle in the front, later it changes to the back, then to the front again. Seen when the groom falls back and grabs the handle, then picks the pirate up and drops him. (00:19:15 - 00:20:05)
Deliberate mistake: When the crow drops Shelley's ring into Sarah's hand at the end of the film, the sound of metal upon metal is heard. (01:30:00)
Deliberate mistake: Even though Hamm is flicking through the channels at the same speed, the side with Al's advert on it is visible for longer.