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.
Continuity mistake: When Kevin bumps into the lady at the airport you see the guy who Kevin thinks is his dad run through the door and out of sight. In the next shot, you see him walking through the door.
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?
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: When the McCallister family arrive at the Florida flight and give in their boarding passes, Sondra is 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: 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.
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.
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.
Plot hole: The sheer distances Kevin covers on foot in one night are outrageous. Between 9pm and midnight he walks from Carnegie Hall to the children's hospital, to 95th street, back to the toy store carrying a large paint can and a large 2x4 (street signs here put it around 59th and 5th), back up to 95th, then all the way back to midtown, to Rockefeller Plaza. One way from W 95th street to around E 59th and 5th Ave. is at least an hour on foot for an adult, he does this 4 times between 9pm and midnight, once while carrying a 2x4 and paint can, once while being chased by 2 adults, and he still has time to set up a house full of traps.
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)
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.
Revealing mistake: Makeup is visible before the first brick hits Marv Merchants.
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: After Kevin pushes Buzz, causing all the singers to fall over, Kate and Peter who are sitting next to each other, both stand up. But in the next close-up shot, Kate is standing alone.
Revealing mistake: When Kevin breaks the pearl necklace while being chased by Harry and Marv, the hands doing the breaking are not Kevin's, they are much too big to be his.
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: 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.
Factual error: There is no pool at the Plaza. Some people think this was the pool at the Four Seasons hotel in Chicago, but that is impossible as Kevin was already in New York City at the Plaza Hotel when the swimming scene takes place.
Answer: He's heading back to the hotel most likely to apologize for spending such a huge amount.