Continuity mistake: When the Antereans go into the sea for about the second time I think, Jack stays on the boat and starts playing about with the machine and makes it go off. When it does he drops a load of sweets or nuts out of the bag he was holding, but when the camera cuts away then cuts back there are no nuts or sweets on the floor.
Factual error: Young David focuses his telescope at the moon. A close up shot then shows a circular view i.e. it is supposed to be the view through the telescope. Both the moon and the clouds in focus. With a telescope the depth of field is short and, with the moon in focus, the clouds would actually be blurred.
Deliberate mistake: David spots the boat with the old folk on and runs around the harbor, down the jetty and jumps towards the dive boat as it leaves the jetty. He doesn't jump very high and you can see he would miss the rail on the boat. In the next shot, a (larger) stunt double is shown leaping high in the air onto the boat and, of course, catches the rail.
Audio problem: When Ben and the rest of his friends are "out on the town", he starts his car to go home, but when he does it makes the distinct sound of an older Chrysler when he was driving a Cadillac.
Continuity mistake: Water in the pool becomes instantly still after the old men get out the first time.
Continuity mistake: David goes with his Grandpa when the old man has his eyes tested. David's hairstyle changes from shot to shot. He starts with a center parting and then has a more dishevelled style.