Continuity mistake: When the kids finally stand up to the schoolyard bullies, a bus parked in the background keeps disappearing and reappearing.
Other mistake: When the family goes to the hardware depot to obtain home improvement materials, the twins manage to imbed the tines of a fork lift into a display of bagged sand over the Admiral's shoulders, yet the entire contents of the ripped bags drizzle down higher, onto his head.
Revealing mistake: When the school bus drops off the children, you can see its front license plate, a Connecticut plate with a "000-AAA" format - which, in Connecticut, is used only on privately owned passenger cars. (Connecticut school bus plates have a "00S00" format.).
Continuity mistake: After landing in the wallpaper paste, Dennis Qauid's face and collar are covered but there is hardly anything on the rest of his shirt. In the next shot, without time for the paste to have dripped, there is a wide swath of paste below his collar.
Deliberate mistake: Frank Beardsley moves his family into an old, defunct lighthouse, and subsequently makes a project of restoring the rotating lamp and actually running it. But lighthouses are navigational devices. Each one in use has its own unique, catalogued period, which identifies it and therefore helps a distant ship determine its own position. By running a "phantom" lighthouse, Frank, a career Coast Guard officer, risks confusing ships' navigators at sea. No real nautical officer would do such a thing.
Revealing mistake: When the kids in the lighthouse tower are pulling the others back up and across the window sill, the unnatural angle makes it obvious that a dummy was being used.
Factual error: The oldest of Frank's sons has the other five boys lined up facing him. He issues the command, "About face!" Each of the boys makes a quarter-turn to the right, which is "right face", not "about face."