Kaeloo, Stumpy, and Quack Quack use a machine to turn themselves into adults. Mr. Cat, who declined to participate, tries to bring them back to normal.
"Let's Play Grown Ups" contains the following tropes:
- Bad Future: Downplayed. The future the adult main four come from is one where they have completely forgotten each other, and Stumpy is a homeless panhandler.
- Bread, Eggs, Milk, Squick: Kaeloo tells the others about things grown-ups have to deal with: taxes, bills, and divorces.
- Furry Reminder: Mr. Cat concludes that talking to adult Stumpy is worse than coughing up hairballs.
- Growing Up Sucks: The basis of the episode.
- Hollywood Tone-Deaf: Kaeloo, Stumpy, and Quack Quack's ability to sing is... less than stellar, to say the least.
- Irony: The episode ends with Kaeloo, Stumpy and Quack Quack singing a song about what a wonderful friend Mr. Cat is to them. At the moment they're singing this, Mr. Cat is running around looking for a bazooka or other weapon to kill them with.
- Split-Personality Takeover: In the future, Bad Kaeloo becomes the dominant form and only turns into regular Kaeloo when angered.
