When Kevin first enters Natalie's house she shows him how to use a smart key by turning off the fire. In the next shot the fire is on again.
After the flood, Kevin can be seen picking up a bottle whilst holding the remote control. In the next shot, he picks up the bottle "again", just before he tried to get the house to tidy itself.
When Natalie first meets Kevin, the strap of her black dress goes from up, to down, then up again.
When Kevin is fiddling with the Christmas presents, the position of the gifts change between shots.
When Kevin floods the lower floor, he is seen standing at the front door and then picking up items floating around. At no point do you see Kevin fall over or get wet. However When Dad calls Kevin for a "talk", his bottom is all wet.
In the scene when the robbers first enter the house, Kevin goes to hide in the shower. It looks like there is only one way out of the shower. How can Kevin possibly get out of the shower, let alone the bathroom, without getting wet after he turns it on?
When Marv and Vera first break in the house, they enter the bathroom through Kevin's room, the door wide open. Kevin turns on the shower and floods the house. Kevin's room would've been flooded as the door was open. However, Kevin leaves from the room, there is no flood.
During the flood, six inch boards are on all the doorways preventing water from flowing into adjacent rooms.
The iron saucepan changes when it's hitting the Marv's head and Vera's head.
When Marv and Vera fly into a chandelier and they hang onto it, you can see the wire is visible.
Obvious stunt double when Kevin is against Vera and Marv.
At the end, obvious stunt double when Kevin is against Vera and Marv.
Although recasting is common in media and film, the characters don't resemble their original counterparts from the first two films at all. Marv especially is given the appearance of a taller Harry and wears almost the same exact attire to him.
When Kevin turns around from the monitor and sees Prescott for the first time, he screams and then it cuts to a different shot a bit too early, cutting the scream off too early as well.
When the police are taking Marv and Vera away, they have a little argument about what prison is like etc, though they are arguing quite loudly, Marv's lips don't move at all, and Vera is still chewing gum.
When Kevin traps the butler in the freezer, says, "One down, two to go," and runs off, the cameraman is reflected in the freezer door.
The left leg of a crew member is clearly visible on the lower left section of the screen at around 58 minutes.
When Kevin cleans the house which is flooded from the bathroom, you can see a crew member reflected on the wall by the door.
When Kevin is pouring marmalade on his toast, the camera pans to the housekeeper and you can see the shadow of the camera on her outfit.
When Kevin is knocking on the door for the Prescott you can see a crew member reflected on the door.
The story take place during Christmas time, yet there are still plenty of leaves on all the trees and the sun.
Though the film is set in Chicago, the palm trees are visible.
The movie is set in Chicago during Christmas. There is a plenty of leaves in the trees. Winter occurs from December to February (approximately) in the Northern Hemisphere. (The movie was filmed in South Africa which is in the Southern Hemisphere where Winter occurs during the Northern Summer).
With Kevin not being the right age for the time the film takes place, neither are Buzz or Megan. In the original film and sequel, Buzz was at least 6 years older than Kevin was (Kevin being 8 and Buzz being at the most 14). However in this film, the actor who plays Buzz is only 14 in the new film. Same with Megan. While being a year younger than Buzz in the original, she is now 12 instead of 14.
In this movie, Kevin is shown to have a teddy bear, which is stated by Peter and Kate to be his most transitional possession and that he can't go anywhere without him. Yet, there is no point in the first two films where Kevin is ever seen to have a teddy bear nor any other toy which he takes everywhere with him.
Kevin has 4 siblings not two no explanation was given about what happend to other brother and sister Linnie and Jeff.
Kate tells Kevin that they're going to do all the things they usually do at Christmas, including putting cookies and milk out for Santa. However, when Kevin did this in the first film the fact that they were still there the following morning should've told him that Santa isn't real, so he shouldn't still believe in him and hence there's no point in Kate suggesting it.
When Kevin is spying on Marv and Vera with his Superspy Bugging recorder, he successfully captures a recording of their conversation to kidnap the prince. Later when Kevin gets into trouble with Peter and Natalie for ruining the party, after Marv and Vera escape, he surprisingly doesn't show them the recording to prove his was being truthful about Marv and Vera's presence.