Continuity mistake: When Laurie gets into Annie's car, she throws her coat in the back. During that shot when both of the girls are visible, the rear view mirror on the windshield between the two of them is level. When it cuts to only Annie and Laurie in the subsequent shots, the rear view mirror is crooked, tilting to one side.
Revealing mistake: When Laurie is kneeling down talking to Tommy and Lindsey, you get a good view of her arm where Michael stabbed her. You can plainly see it's just a streak of stage blood with no cut at all.
Continuity mistake: In the scene where Laurie walks across the street to check on her friends, the porch of the Doyle house has nothing on it. When Laurie runs back across the street and starts pounding on the door she picks up a flower pot off the porch to throw at the window. (01:11:20 - 01:18:30)
Continuity mistake: When the girls are walking home from school, Annie says that she is babysitting Lindsey Wallace and Laurie says she is babysitting Tommy Doyle. Laurie also claims that the Wallace's and the Doyle's house are 3 doors down, but when Annie drops Laurie off the houses are right across the street from each other.
Visible crew/equipment: Just after Michael has picked up the knife, a stage light can be seen in a silver pot. This is as he walks into the next room. (00:04:15)
Continuity mistake: Annie's underwear changes patterns from a beige color to a floral pattern when she's stuck in the window.
Continuity mistake: When Laurie is in the bottom of the closet hiding from Michael, you can see that a purple dress is in front of the rest of the clothes. However when she stands up to grab a hanger, a pink sweater is in front only to be behind the purple dress again when she sits back down.
Continuity mistake: When Annie takes Lindsey round to watch TV with Tommy, they leave the TV in their house on. But when Annie comes back looking for her car keys, the TV is off.
Visible crew/equipment: During the opening sequence, the scene is shot in first-person point-of-view from the young Michael Myers. As he walks through the house, the shadow of the camera can be seen several times. After he picks up the knife in the kitchen, the camera's shadow is visible on the door frame leading into the dining room. It can be seen again just before he turns to go upstairs. (00:04:05)
Factual error: It's supposed to be late autumn, but in most scenes the leaves are still very green. [This is because it was shot in California during the summer. Carpenter imported leaves for every shot that you saw leaves blowing on the ground and blew them with a giant fan (this also killed any ambient sound takes); there are also a few shots where you can see palm trees (most prominent the one right in the front yard of Michael Myers' house).]
Continuity mistake: After Laurie asks Annie what she is going to wear to the dance (while Annie is driving with Laurie), we see Annie turn the steering wheel to the left, yet the car turns right as seen on the green screen in front of them. As the car is turning right, it cuts back to Annie still turning the steering wheel left. (00:33:45)
Continuity mistake: Toward the end of the movie, Dr. Loomis comes up the stairs and starts to shoot Michael six times, sending him spiraling to the terrace. Take notice that Michael is about to go over the ledge of the terrace head first. In the next shot it shows him carefully backing off the ledge, while facing the house. (01:26:45)
Other mistake: When Annie goes to get her car keys, notice she goes through the back yard and goes to the front of the house as if the garage is in the back yard, when we see the garage on the left side of the house.
Continuity mistake: When Lynda is talking about how she forgot her books (at the beginning of their walk home) we see Michael Myers drive by, then speeds up and drives passed a driveway, then it cuts to Annie (Myers is still driving) and she says, "Hey Jerk. Speed Kills." We see Michael driving again and he is just a bit behind the drive-way he drove by before, he should be much farther ahead down the road at the speed he was going. (00:21:35)
Continuity mistake: The young girl walks up to the Myers house near the start. From the view in the house she reaches the door. Camera changes and she's halfway up the steps. (00:13:20)
Revealing mistake: In the scene outside of Smith's Grove mental institution, where Michael jumps on top of the station wagon, he attacks the nurse, but she manages to wrangle free. A few moments later, he smashes the passenger side window. If you look closely, the actor's arm has a wrench taped to it in order to effectively break the glass injury free. (00:10:30)
Visible crew/equipment: When Michael's POV shows him turning around the house to look upon the lights from his sister Judith turning off, some set lighting cables are visible coming out from the window and lying on the ground in the house porch. (00:03:20)
Revealing mistake: Towards the end, Laurie pulls off Michael's mask, revealing his distorted face, but as he pulls the mask back down, the distorted face is also a mask as you can see the seam around his neckline.
Visible crew/equipment: When Bob gets impaled, Michael steps back to observe. Crew lights are quite visible behind Michael's head as the camera pans back. (01:05:50)
Revealing mistake: When Annie is putting her clothes in the wash the door slams shut and she walks over to try and open it, look closely and you can see her turn the deadbolt and lock it so she can't open it. (00:46:45)
Answer: There are only two families that hire babysitters in the film, the Doyle and Wallace families. Where they went is never explained, but it could be potentially anywhere. They could have gone on a trip out of town for the night, they don't have to be in Haddonfield.
BaconIsMyBFF
Where did it state this was all night? It could have been a few hours. Remember that in the next one, it is still the same night and stays night through the entire movie.