Continuity mistake: When Dave gets off the bus when they are on the field trip you will see a man with a purplish shirt on and a woman with a yellow jacket on with a baby stroller, later when the teacher is done saying what he was saying, Link will go looking around by himself. If you pay close attention you will see the man and woman again except for this time they don't have a stroller.
Continuity mistake: Watch the scene first of the movie when the science teacher is explaining about cavemen closely. He writes the words 'Cromagnon Man' on the chalk board, pulls down a diagram, and proceeds to walk around the classroom. A few shots later, after he comes back to the chalk board and raises the diagram, the words have changed in both size and position on the board.
Continuity mistake: In the begining, when Link is in the cave with his wife as the earthquake hits, he is wearing many layers of animal skins to protect him from the cold. The ice buries him and we move ahead to the present day. When the ice-block cracks open during his thaw-out in the boy's garage, he is only wearing a tiny g-string arrangement. What happened to his animal skin clothes?