Other mistake: In the scene where Kevin is making the hotel reservation on the phone, the lady does not even ask the dates of when he will be arriving and leaving the Plaza.
Other mistake: When Kevin first enters the hotel, he is told to get to the lobby he should go straight ahead and turn left. The next shot shows him turning right into the lobby.
Other mistake: When Kevin jumps off the hotel loading dock, Harry has his hands up. This displays the 'M' burnt into Harry's palm in the first movie. The 'M' should have been sideways because he grabbed the hot door knob at 90° in the first film. Same mistake is in the first film.
Other mistake: When Marv ends up stepping on some green gunk that Kevin set as a trap in the basement, he eventually slips and then slides into a shelf of paint. However, Marv actually started sliding after he fell to the ground. It's almost as though he was being pulled forward. How could he have slid?
Other mistake: When Kevin is checking in, the time on the clock behind the front desk lady doesn't change from 2:52 over the whole course of time that he's checking in.
Other mistake: In the scene where Kevin is being chased through the Plaza lobby, the large brass/marble table, usually in the center of the room, has been moved to one side to allow the characters to freely run through the area. The table has been purposely moved as it is right next to the concierge desk which would pose an inconvenience to any guests and so, therefore, is not a natural occurrence. After all three fall over, it is evident that a large space has been cleared, as it allows for Cedric to be dragged away as well.
Other mistake: When the McCallister family is in the Chicago airport and Kevin is changing his batteries, on the P.A it says that American Airline flight 226 to New York is in the final boarding process, and Kevin runs after the man who is running to the gate. Once they are on the plane, the flight attendant announces, "Welcome aboard American Airlines flight 176 non stop service to New York." These are different flight numbers. (01:26:00 - 01:40:00)
Other mistake: At the start of the film, Kevin tapes his Uncle Frank singing in the shower, but he doesn't tape all of the singing. When Kevin is in the hotel in New York, he plays back the tape when the blow up clown is in the shower, all of the singing is on the tape, including something his uncle said when Kevin ran away from him.
Other mistake: While Kevin asks the ticket agent in New York what city he's in, there are signs at the gate indicating departing New York LaGuardia and destination Los Angeles. No gate at any airport would have a "departing" city sign - only destination city. Travelers know what city and airport they are physically at and leaving from.
Other mistake: The old man that receives Kevin's bag in Florida can be seen walking through the airport when the family runs past him. The man could not have boarded the flight to Miami, as the family ran past him and were the last to board. The man was wearing shorts when he received the bag (but he could have changed on the flight in theory - had he been able to board). An old woman with him was in the same situation. (00:12:52 - 00:17:36)
Chosen answer: Remember that Kevin didn't give his name, nor did the police ever see him. When he called, it was from a different address and he gave his name as "Murphy." There is no reason to think that Harry and Marv would tell the police about Kevin, since they would have to admit being outsmarted by a child and also admit to kidnapping, assault, battery, and a wide array of charges for what they tried to do to him. Even if he did testify, there is no reason to think his parents wouldn't know.
Greg Dwyer
And by the way Kevin knew nobody would believe him.
Not entirely correct - He rang the Police from the phone in his parents bedroom just before the spider scene.