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: 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: In the facial morph, the faces don't come anywhere close. The face was morphed with no feature of either resembling the other. The only matching features were the hair and neck which were not touched by the morph. The midpoint of the shift wreaks of Photoshop-like effects (softening of the face alone). (00:41:50)
Deliberate mistake: In the scene where Mr. Bean is hitch hiking, right before the shot where the truck runs over the wooden box, there is a wide angled shot. The road is very long and it is clear that there is no truck coming. In the next shot, the truck suddenly zooms by from the right of the screen. This can also be seen on the trailer. (00:44:30)
Deliberate mistake: After Sharpay falls into the pool, when Gabriella dives in it is an obvious stunt double for the actress. (00:16:40)
Deliberate mistake: In the housing block that Dave's house is in, the house numbers do not match - because In one shot of Claire walking past Dave's house, you can see that the house numbers are in the 1500's - one homes number is clearly 1516. However Dave's house number is 1958. However this is a deliberate mistake as the 1958 on Dave's house is a reference to when the Chipmunk fever was born. (00:23:50 - 00:32:35)
Deliberate mistake: In the fire scene, Jon tries to catch Garfield from the chandelier at the main staircase. When Jon reaches out to grab Garfield, there is no rail on the stairs. It comes back in the very next shot & disappears again after Garfield says "Need a lift?"