Other mistake: When Dr Grant and the children reach the perimeter fence, Dr Grant tries to see if he can fit through, to no avail. When he and the kids start to climb, however, it is quite obvious that both Tim and Lex would have been able to crawl through quite easily, and that only Dr Grant should have had to climb over. Partly this links to the mistake here, where the holes in the fence are much bigger in the first shot, then when he tries to widen them he's holding a different part of the fence where they're smaller.
Other mistake: When Grant and the children are up in the tree, as Tim is telling his jokes the camera pans out and we get a wider view. In this shot you can see that Grant's boots are spotlessly clean, which is highly unlikely given the muddy ground, wet environment and his activities over the past few hours. (01:20:35)
Other mistake: When Alan, Lex and Tim are climbing over the perimeter fence and the buzzer begins to sound, Alan and Lex have come off the fence on the other side and Tim loses his footing further up on the fence. He begins to pull himself up, but in the very next shot, a person is seen coming down the fence closer to the ground in khaki shorts and boots. Tim hasn't moved from his position further up, so it can't be him, and Alan and Lex were already on the ground, and did not have khaki shorts on. (00:43:15)