Continuity mistake: When the kids are gathered to film on the hill with the train crash in the background, Joe grabs the camera to get a closer look, setting up the tripod a couple feet away from Alice. Joe hunches forward to look through the camera. Then the group is shown from behind and Joe isn't hunched forward anymore. Alice is still a couple feet to the right and Cary a couple feet and forward to the right of her. When the camera comes back around to the front of them, Joe is hunched forward again, and Alice & Cary are right next to him.
Continuity mistake: When the kids break into the school and discover the footage of Dr. Woodward and the other scientists, they break a window on the classroom door. The glass is almost completely removed from the frame but once the military arrive and take the kids away, there is suddenly more glass in the frame.