SpongeBob SquarePants Season 5 Episode 24

Plankton’s latest scheme sees him invent a gas that causes people to turn into babies. Plankton hijacks the Krusty Krab and turns all the customers into babies. Plankton then gets the secret formula, but SpongeBob accidentally overpowers the gas canister by bashing it, causing it to explode. The gas turns Plankton into a microscopic baby.