Continuity mistake: When Kevin is buying some toys at Mr. Duncan's Toy Store, he pays for the toys and there is a can full of pencils to the right of Kevin. As the camera switches shots to Mr. Duncan and back to Kevin, the pencils are in different positions every time.
Continuity mistake: In the final scene, Kevin approaches the pigeon woman. She says "Merry Christmas" without any pigeons on her head. The long shot is taken, and she now has at least four pigeons are sitting on her head. A close-up is taken when Kevin approaches and reaches her hand, and again, pigeons have disappeared from her head. Impossible to have the pigeons flying on and off her head in the space of half a second.
Continuity mistake: When Kevin is throwing bricks from the top of the apartment building, note the position of the gym bag beside Marv - it is in the wrong place, positioned differently, during one of the cutaway shots between Marv and Kevin.
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?
Revealing mistake: In the scene when the bandits are in the uncle's house at the bottom of the stairs, the tool chest falls down. When it hits the door and they slide back if you look closely you can see that they are on rollerblades.
Continuity mistake: When the McCallister family arrive at the Florida flight and give in their boarding passes, Sondra standing in front of the gap between the man and lady taking the tickets, and then leaving. In the next shot she is standing in the same place again and leaving a second time. (00:12:55)
Continuity mistake: After Kevin throws a few bricks off the roof, a brick is lying at Marv's feet. In the next shot, it is gone. When Harry disappears, we see three bricks, all on the road and none by Marv.
Factual error: The picture that Kevin takes of Marv and Harry through the toystore window is perfectly clear. There is no way you can take a picture of something through a window without the flash reflecting back and ruining the image, especially from as close a range as Kevin was.
Revealing mistake: When Kevin arrives at the airport in New York (filmed at Chicago O'Hare) and goes up to the agent to ask her what city is outside the window, one of the destinations on the board at the gate is New York - LaGuardia...giving away that the scene was not shot at a NYC area airport.
Visible crew/equipment: As Tim Curry exits the lift to secretly search Kevin's room, at the bottom right hand corner a shadow that looks like a hand appears on the wall to the left of the lift, inconsistent with the movements of him exiting the lift. You have to be quick, as it appears on widescreen as the shot moves away from the lift doors.
Continuity mistake: When Harry and Marv catch Kevin for the first time, coming out of the hotel, they walk away and are standing at the traffic lights. The camera angle is Kevin looking up at Harry and is from below Harry's elbow but Kevin's height makes this impossible seeing as he is up to Harry's shoulder.
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.
Continuity mistake: Kevin is being served ice cream in his hotel room. A wide shot of the bed shows the food around it and the waiter scooping ice cream into a bowl. Look at the tall pink rose at the end of the bed, which towers out of its vase. In a couple of shots later, the rose suddenly becomes barely higher than the vase itself. (00:33:30)
Continuity mistake: Take a look at the position of the penknife when Kevin is paying for the toys and chatting to Mr Duncan. In one shot it's in line with the camera, on its front. The next shot (10 seconds later) the penknife is on its side and lined up with the book. Mr Duncan did not touch them in this time.
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)
Continuity mistake: When Marv has just climbed out of the basement through a hole in the floor, we see him dangling facing forwards, but the shot of his legs below gives the impression he's facing sideways. He has no time to switch positions between both shots.
Continuity mistake: When the McCallisters are at the police station, the cop puts downs the phone and tells them there is "No sign of him." Behind them, the coffee pot is half full and a lady in a multi-coloured top talks with another cop. In the next shot of the McCallisters, the coffee pot is almost empty, a coffee tin with a red lid appears (that was taken away in an earlier shot) and a completely different lady talks to the cop behind them.