Other mistake: Max says that Michael is the "Man of the house" and won't come in until he's invited, which Michael sarcastically does, except Michael isn't the man of the house - its actually his grandfather who owns it.
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)
Continuity mistake: Near the middle of the film we see that Michael has a transparent reflection in a mirror because he is a half vampire. Yet, earlier in the film when the other vampires, who are full vampires, are in the video store, their reflections can be clearly seen in a glass counter. (00:12:10)
Continuity mistake: When Michael first comes home after becoming a vampire he gets some milk out of the refrigerator and when he collapses the whole top of the carton busts open but when his mom comes home and picks it up only one side of the carton is open. (00:37:45 - 00:45:40)
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)
Continuity mistake: About 45 minutes into the movie, when Michael is floating on the ceiling then out the window, he knocks the phone off the hook. The phone then rings and Sam answers. (00:42:55)
Visible crew/equipment: When Michael is closing the windows when the lost boys are going to attack the house, he passes in front of a cabinet and you can see the reflection of a crewmember on the glass.
Continuity mistake: The family dog bites Michael on the left hand in order to "protect" Sam, which leaves a nasty, bloody gash. As Michael runs up the stairs to talk to Sam, he leans the palm of his left hand on the railing a couple of times for balance. There are no bloody hand marks when he picks his hand up. (00:40:00 - 00:40:45)
Continuity mistake: In the scene at the beginning of the movie where the flying vampires are chasing the security guard across the boardwalk parking lot, the positions of his arms as he is running changes back and forth between shots. In the close-ups of the guard's face, his hands are up, holding his hat down on his head. In the wide shots, his arms are down at his side. (00:02:45)
Continuity mistake: When the mother is leaving a bottle of wine at Max's house and is being chased by the dog, the dog lunges through the fence. The fence slightly breaks apart by the dog's mouth. The shot changes, and the fence is intact. Another shot and the fences has an even bigger gash in the side, and again, intact.
Continuity mistake: During the opening we see Michael, Sam and their Mom enter the town and check it out. Michael asks a man if there are any jobs in town. The next time we see Michael he's taking his motorbike off the trailer. Then we see him in the car for one shot. When they reach Grampa's house he is riding the bike. (00:04:55 - 00:06:05)
Continuity mistake: When Max comes over for dinner, and the boys are testing him to see if he's a vampire, Sam spills water on him. As the scene progresses between the liquid spill and Max kissing Mom goodbye, at times they change in size/location.
Visible crew/equipment: A harness is visible when Michael is floating in his room.
Continuity mistake: When Sam is taking a bath, at one point the bottle of shampoo is there and then missing when Michael enters the room. Then when Sam pops up from under the water, after Nanook attacks Michael, he grabs a blue towel to wipe his face. There was no blue towel previously in the scene, only a yellow one. (00:38:35 - 00:58:45)
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)
Continuity mistake: At the very beginning of the film, the family is driving towards "Santa Carla" (for which the town of Santa Cruz stood in) from the south along Highway 1. Then a few cuts later and all of a sudden they're driving in the opposite direction, this time from the north along Highway 1. Also, neither of those routes would be the one someone would take from Arizona.
Continuity mistake: In the cave scene David takes a bite of the noodles which are dry, but when he hands them to Michael they are wet noodles. You can even hear the crunch when David first takes a bite of the noodles. (01:00:00)
Answer: In the film, being invited in isn't a requirement to enter. It's simply a way for the vampire to render you powerless (i.e. the tests the boys performed on Max).