Continuity mistake: When nurse Karen first enters the hospital and changes into her uniform, she's clearly shown putting on a dark belt (either black or brown). However, in her next scene with Mrs. Alves, as well as the scene where she's tricked into entering the hospital room to fool around with Bud, the belt is white.
Continuity mistake: When Laurie leaves the hospital, she exits out of the hospital doors. Somehow the doors stay open. Later on in the far away shot, the doors are closed, then they are open again in the next shot.
Continuity mistake: Towards the end of the film, when Dr. Loomis finally finds out Michael is at the hospital and orders the trooper's car to turn around. As the car turns around, the lighting outside appears to be pre-dawn however they arrive at hospital and it is still pitch black.
Continuity mistake: When Pamela Susan Shoop is being killed by Michael in the spa, the towel is tied arround her upper chest, then the towel falls down, revealing her breasts. In the next shot a split second later the towel is back up at he upper chest.
Continuity mistake: When Michael falls off the balcony, he falls into some green grass and a garden is next to him. Yet in the original "Halloween", Michael falls onto the ground with barely any grass around him, just a dirt patch and no garden in sight. (This is explained because they reshot the ending to "Halloween" 1.).
Continuity mistake: After getting out of the car, Laurie is on the ground beside Jimmy's car outside the hospital when she sees the Marshall's car pull up. When Loomis tells the Marshall he ought to handcuff him to the wheel, if you look, Jimmy's car is still visible in the distance, but Laurie is not in that shot.
Continuity mistake: In the scene where the boys ask Mr. Hunt about Ben Tramer, Mr. Hunt says that "it's just a little past 11." Following this up in the next scene Bud lures Karen into the room to kiss her and wish her Happy Halloween. During this scene, as Bud reaches up to kiss Karen, his watch is clearly visible and shows the time as 1:00.
Continuity mistake: The flashing lights on the front of Bud and Jimmy's ambulance change places as they pull into the hospital driveway. They go from either the side of the hood to the front of the bumper.
Continuity mistake: Michael falls from the balcony in a different way from the first film.
Continuity mistake: Michael comes into Laurie's room and stabs at her bed, only to find pillows had been placed there. He then walks out and leaves the door open. When Jill returns from checking on a patient, the door is now closed and she opens it.
Continuity mistake: In the first scene when Loomis has just shot Michael. In first film, Loomis looks over the balcony and see that he is gone, but now he goes out and discovers that he is gone.
Continuity mistake: When Michael walks into the old couple's house, NIGHT OF THE LIVING DEAD is showing on the television. At that point, the film is just beginning, with Barbara and Johnny first pulling up to the cemetery. Much later in the film, the security guard is also watching NIGHT OF THE LIVING DEAD on television, and it's the scene where the cemetery zombie is attacking Barbara in her car. This is no more than ten minutes later in NOTLD, yet it's way more than ten minutes later in the evening of HALLOWEEN II.
Continuity mistake: At the end of the first film, Dr. Loomis looked down from the balcony to find Michael's body gone. However, in this one, he finds the body missing when looking out of the house's front door.
Continuity mistake: When Laurie runs away from Michael Myers in the boiler room, she climbs a window and falls into a storage room. Her hospital gown gets flipped as she falls, exposing her underwear. The close-up shows her falling again, this time without the upskirt shot.
Continuity mistake: Nurse Jill turns around before Michael Myers stabs her. After she's stabbed, she's already facing forward and her head doesn't snap to face the camera.
Continuity mistake: After Nurse Karen is drowned by Michael Myers, he drops her backward. The close-up shows however that she falls forward.
Continuity mistake: The front door on the Doyles' house is different from the one seen in Halloween. You can see this when Dr. Loomis leaves the house in the beginning of the movie.
Continuity mistake: After the guy in the hospital slips in the blood puddle he has some blood on his face and mouth that disappear between shots.
Continuity mistake: After Loomis and the police officer see the fake Myers they leave the car with the doors closed but in the open view they are open again.
Continuity mistake: After the hospital guard takes a look outside he checks the trash container which has inside a box with a big bloodstain which disappears in the next shot.
Answer: I have read that, in early drafts of the script, the hospital was a health clinic, not a standard hospital. This would possibly explain why there are only a small number of patients, though it doesn't explain why there is a maternity ward, or why the mother brings her son there for emergency treatment.