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: 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.
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 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.
Continuity mistake: When Diane sees the creature in front of the door and yells "No - don't hurt my babies!" she crosses in front of it and falls down the stairs. When she's in front of it you can easily see the creature's eyes and mouth through her, on her shirt.