Other mistake: In the first shot when Carol Ann is being put to bed, the wicker headboard is backwards. I know this for a fact because I used to have the exact same headboard (queen size), and the large support frame faces the wall. The only thing you're supposed to see is a bunch of single swirls in the front. But they probably turned it that way so Carol Ann would have something to grab onto. White wicker furniture was very popular and cheap in the 1970s.
Continuity mistake: At the start of the film, the dog is seen going from room to room looking for food. Just before he goes into Dana's room, someone can be seen through the crack in the door, moving from left to right.
Revealing mistake: When the chair moves across the kitchen floor, Craig T. Nelson goes to investigate it (after it has stopped moving). He goes up to the chair and flips it over. If you look closely, Craig almost hits the camera with the chair's legs. You can tell this has happened because the camera moves up very quickly and Craig looks straight at the camera crew with very big guilty eyes. This is more easily visible on the widescreen version of the film. (00:33:30)
Continuity mistake: When Carol Anne is being sucked into the closet vortex she clearly lets go of the white wicker headboard of her bed. In the next shot, the child (actually a dummy or a stunt double) is seen sailing into the closet, grasping a sizeable section of the now broken headboard.
Continuity mistake: When the scientist's face starts to melt, the stuff on the wall keeps changing all the time.
Visible crew/equipment: In the breakfast scene when Robbie's milk glass spontaneously shatters from the bottom. Watch closely, you can see a string coming out of his cereal bowl and attaching to the bottom of his glass. Robbie just needs to give the glass a little tug, and splash.
Visible crew/equipment: Near the end of the film, when she lands behind the stairs. If you look in the right hand corner, underneath the stairs, you can see tennis shoes running by.
Continuity mistake: Robbie watches the tree and gets in bed. Next to him there's a yellow comic book underneath a Darth Vader bust. When his mother arrives the comic book is completely different.
Continuity mistake: After Diane places the chair to show Steve how it moves, the chair swaps from being parallel to him to slightly skewed. Also, its position on the floor changes: First the right legs aren't touching the brown lines, and a frame later they are.
Continuity mistake: In the opening sequence while the kids are in bed, the toys on Robbie's headboard keep changing. The Rams football helmet is always there, but next to it, you will see a Star Wars droid, a Rubik's cube, a race car, or a dinosaur, depending on which shot it is.
Continuity mistake: The wicker headboard of Carol Anne's bed is ripped apart when she holds onto it to try to keep from flying into the closet. Towards the end of the movie, when her mom tucks her into bed, the headboard is intact and has had no repairs.
Continuity mistake: Toward the end of the movie, as the family gets in the car and leaves, the garage door is closed on the house. But when the house begins imploding, suddenly the garage door is wide open. (01:48:10)
Continuity mistake: As Diane brings the freshly-washed flask to Dr. Lesh, who's sitting at the kitchen table, the flask jumps from one hand to another.
Continuity mistake: A few seconds after Steve stops the car for his daughter, Robbie yells. During this brief scene you can see a bluish flannel on Robbie. About eight seconds later, Robbie's red pajamas reappear. Previous to these scenes, Robbie was wearing his red pajamas.
Continuity mistake: When the men are watching football, they are reacting as if they are watching live action. However, the images shown on the TV are clearly in slo-motion.
Revealing mistake: When the father tucks Robbie in and Robbie says "I don't like the tree, dad." the camera shot begins rolling to the left. Robbie flinches when reacting to someone telling him to lean back more so he's not blocking too much of the father's face. The father also improvs a solution by gently pushing Robbie's shoulder back a bit as well. (00:18:55)
Continuity mistake: When the mother falls into the muddy swimming pool, and the bodies are popping out from the ground,she was drenched and covered in mud. By the time she runs upstairs, she is almost completely dry and there is very little mud on her.
Continuity mistake: After the chair moves, Steve is in awe, his left hand on the counter. A frame later, on the close-up shot, it's on his thigh.
Continuity mistake: When the kids are sitting around the table saying, "Ask Dad" right before Robbie's glass breaks, he picks up the glass twice in two different shots.
Continuity mistake: When they put Diane and Carol Anne into the bath tub, near the end of the film, look at Carol Anne's face. The red gunk changes in pattern every time we look at it.
Suggested correction: Diane could've bought a new headboard obviously.