Continuity mistake: In the scene where Tom Hanks goes back to his mother's house when he's "BIG", he tries to convince his mother it's him by telling her his birthday: November 3rd. However, in the scene (with John Heard and Elizabeth Perkins) showing the milk carton of Tom Hanks "missing" as a young boy, his d.o.b. is shown as 1/20/75.
Continuity mistake: When the camera first pans up to Josh on the top bunk as "big," note his coat on the bottom bunk: The letters on the back are pushed together and three are barely visible. Yet when he returns from the bathroom moments later the coat is noticeably more spread out and many more letters are visible.
Continuity mistake: After Josh makes his wish, a shot depicts the older kids run behind the tents. During this shot, the camera shows a side view of the Zoltar machine. You can see the head stop moving up and down, and the breathing sound continues. After Josh reads the card, the head is moving again.
Revealing mistake: At the end of the movie when Josh and his friend are walking down the street, a lady crosses the street in front of them. Look closely to the left of the screen. The lady is obviously behind the tree waiting for her cue because she is not seen walking toward the tree before crossing the street.
Continuity mistake: When the shot first enters the bedroom the morning Josh becomes big note the yellow truck at the foot of his bed, it is away from the lower left corner and facing out. When Josh jumps down from the top bunk it is flush with the bunk and facing the other (right) foot of the bed and remains in this position for all remaining shots of the bedroom.