Continuity mistake: Michael is watching Annie in the kitchen. He knocks down the hanging plant in front of the door and it shatters. When Laurie goes to check on her she goes in the same door and the plant is hanging back up. (00:43:21 - 01:12:56)
Revealing mistake: When Tommy is trying to show Laurie that Michael is outside, something to the left of the Wallace house looks like legs moving around in the dark and then jumping up. Presumably, this is Nancy Kynes jumping up into Tony Moran's arms so that he can carry her around the front of the house, which is actually the shot that is used about ten minutes later. Carpenter potentially used this shot of the house either unaware that they could be seen, or didn't anticipate the future change in aspect ratio. (00:45:30 - 00:55:30)
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)
Visible crew/equipment: When Annie is locked in the laundry room, there's a scene where the phone is ringing incessantly and the camera pans slowly to the right showing little Lindsay Wallace who's too busy watching television to answer the phone. If you watch this scene in widescreen, you'll see a crew member lurking in the shadows (left side of the screen) on the wall. It appears they are trying to avoid being seen. (00:47:10)
Continuity mistake: In the scene when Michael is carrying Annie's body into the house her head is on the left side of his body. After they show Tommy looking out the window they cut back to Michael and suddenly Annie's head is on the right side of his body. (00:55:14)
Continuity mistake: When Bob and Linda arrive at the Wallace house, the exterior shots show the doorknob on the front door to be on the left side which would mean the door would swing inward to the right. However, when the shot cuts to the inside of the house as the door opens, the door swings inward to the left and the doorknob is now on the right side. (00:59:20)
Visible crew/equipment: After Lynda and Bob make out on the couch, they both start to go upstairs. Lynda trips over the dolly track and Bob steps over it. (01:01:50)
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)
Other mistake: Immediately after the scene where Laurie is talking to Linda while she is being strangled by Michael, Laurie looks out the window and sees the LOWER level of the other house lights turned on. Michael was on the upper level and could not have gotten down the stairs to the first level in time (1 or 2 seconds) to have turn on the lights. (01:08:20)
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)
Factual error: In the scene when Laurie gets stabbed by Michael in the arm she falls over the banister - the camera shows a view of what she sees, falling at that angle Laurie would have broken her neck, spine and hip. But it is still weird how she managed to turn 180 degrees in such a short fall. (01:16:40)
Continuity mistake: When Laurie escapes the house by smashing a window pane, the glass shards disappear instantly in the next shot. (01:17:47)
Continuity mistake: When Laurie is beating on the door to Tommy's house and telling him to open it, the door knob is on the right side of the door. When it shows Tommy opening it from the inside, the door knob is also on the right side (it should be on the left). (01:18:35)
Visible crew/equipment: Just before Laurie stabs Michael with the knitting needle you can see that one of the window shutters is open and that the wind is ruffling the curtain. When the camera gets closer and the curtain is out of the way you can see the huge fan in the studio being used to simulate the wind outside. (01:19:50)
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: At the start of the film, Michael was 6 years old. It's exactly 15 years later when he gets out on Halloween night again which would make him 21. However the ending credits state the two Michaels as 6 and 23. (01:29:00)
Continuity mistake: When Annie and Laurie leave the hardware store to go to their babysitting jobs it is broad daylight. When they reach the houses apparently just a few blocks away, it is already dark.
Continuity mistake: During the beginning of the movie, when Laurie is talking to the police officer, the sun is shining bright as if it is a perfect day, then when Laurie walks to her house, the trees look as if it has just quit raining.
Factual error: There's no way that the knife that killed Bob was long enough to go through his body and impale the wall behind him. And a butcher knife cannot "pin" a human body to a wall and just stay put, they aren't strong enough.
Revealing mistake: When Tommy is carrying the pumpkin from school, you can see it has a cut in it to make it crack open when he falls down.
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.