Other mistake: Toward the end, Genius and Wolf (the dog) are in the lab, Genius suddenly shouts at the dog, "Hey, don't do that. Keep away." The dog wasn't doing anything except wiggle his ears a little. He made no move whatsoever toward the glass jar Genius wants him to stay away from.
Other mistake: When the teens first grew into giants, their clothes did not grow with them, so they had to make improvised clothing out of theater curtains. In the end, when exposed to the shrinking gas, the teens become their regular size, and the improvised clothes also shrink with them. No one else's clothes are affected by the gas in this way.