Continuity mistake: In the first film, it is mentioned several times that Kevin is 8 years old. However, in this film it is stated that he is 10. When his parents are in the Miami airport security office, they say that he was left alone last Christmas. That would make him 9. Both films take place the same days, from about three days before Christmas until Christmas morning, so even if Kevin is born around Christmas time this is still a mistake.
Continuity mistake: When Kevin is running away from Harry and Marv he buys strings of pearl necklaces, and pulls them apart on an icy corner. When the bandits slip on them, there are more pearls there than Kevin dropped.
Continuity mistake: When Kevin throws a rock through the front window of Duncan's Toy Chest, the alarm sounds and Harry and Marv run out of the store. In the next shot, the alarm that could be heard has mysteriously stopped. (01:17:39)
Continuity mistake: When Kevin is first watching the movie in the hotel room the room service guy already has two scoops of ice cream in the dish and is putting in a third. Then later in the scene the guy asks, "Two scoops, sir?" and only one scoop is in the dish and is just putting the second scoop in.
Continuity mistake: When Mrs. McCallister receives the phone call about the police finding Kevin, as soon as she answers the phone, notice the white shirt behind her on the bed. When she tells the family they found him, the camera goes back to her and the shirt is in a totally different position.
Continuity mistake: In the scene where Harry and Marv are at the skating rink, the front of Marv's hair is constantly changing from shot to shot. It's either poofy or pulled back due to the earmuffs he's wearing.
Continuity mistake: When the robbers are in Duncan's Toy Chest at midnight, Kevin sets up his board on the bucket outside the window. He then knocks on the window, takes the robber's picture, then runs back away and pulls a rock out of his pocket to throw through it. But he wouldn't have been able to run back that far without jumping over the bucket and board, and he did not jump or avoid any obstacles.
Continuity mistake: Once Kevin and the attendant board the plane to NYC to make sure Kevin's family is on board, there is a shot of Kevin while he says, "There's my dad over there." In the background, a man is sliding his black coat off of his shoulders. Two shots later when the attendant says, "Well, go find an empty seat," in the background you will see the exact same man taking his coat off a second time.
Continuity mistake: At the pageant scene, when Kevin turns to attack Buzz, you see him make a fist; but when the camera shot changes to include the full choir and the audience, you see Kevin push Buzz with a open palm.
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.
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 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 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.
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: 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 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.
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.