Revealing mistake: When Michael is trying to keep up with Kiefer Sutherland et al along the beach towards Hudson's Bluff, you can see the tyre tracks from the camera vehicle in the sand. (00:21:35)
Revealing mistake: When Alan Frog is reaching for a stake off of Edgar Frogs back the stake is a "trick" stake. He pulls it facing upward and the tip falls down into the stake. As he lowers it off camera he flips it downward and then shows it again and the tip is back out. (01:10:35)
Revealing mistake: Look closely at the footage when the vampires are entering the cave. Later when they are exiting the cave, the waves are flowing backwards. The same footage has been reversed. (01:17:05)
Answer: Because the Head vampire, Max, had fallen in love with Michael's mom. At the end of the movie he said, "Boys need a mother and if I could get Michael and Sam into the family, you would have no choice but to join us."