Continuity mistake: In the airplane, the window shade in the seat next to the main character repeatedly opens and closes between shots.
Continuity mistake: After the old folks turn into kids, Harry, the boy with the glasses, is seen climbing up the side of the house, yet in the next shot, he is running through the bushes toward the camera.
Answer: They'd already filmed most of the episode. The stunt was one of the final scenes to be filmed. They were able to work the story around any missing scenes.