Timmy’s finally big enough for Flappy Bob’s Learnatorium’s “Big Kids” room, which means he’s chased by Francis who wants to welcome him with a beating. So Timmy hides in the Flappy Bob’s Baby Care Room by wishing he was a baby again. Now Timmy’s got a new set of problems. He can’t talk and wish himself 10 again and Happy Peppy Gary, Peppy Happy Betty are his baby counselors, and he must get himself back to his normal age before his parents get back or he'll be stuck there forever!
The episode starts with Timmy at his house. He can't be babysat by Vicky because of what happened yesterday. Timmy wished that Vicky's head would swap places with a fish's head. With no Vicky to babysit, his parents suggested they bring him to Camp Learnatorium, but this time to the big kids' room. It is mostly filled with bullies, including Francis. Francis shows Timmy around while at the same time giving him an atomic wedgie. He explains that the big kid's place is a place where bullies mostly abuse the little kids, including Pops, who was left in the Learnitorium 60 years ago and his parents never picked him up. Timmy manages to escape from Francis and hides in the babies' room. But with Francis ready to tear the place apart looking for him, Timmy desperately wishes that he was a baby. This works to his advantage, as he barfs over Francis and the latter is kicked out of the baby room by Happy Peppy Gary and Betty. Francis is also put in a locked box. However, things get really tough when Timmy discovers he can't speak, and thus cannot undo his wish.
Fearing that if his parents don't find him when they come to pick him up he'll end up like Pops. Timmy tries spelling out his wish with blocks, only to Gary and Betty to constantly interfere until Timmy wished them away to an alligator habitat at the zoo. However. they return before he can undo his wish. Despite Timmy's resistance, he is swaddled in a blanket and put down for naptime with the other babies. However the other babies free him before constructing a gigantic robotic Francis, which they use to storm the big kids area and occupy the bullies. Timmy makes it to the license-plate maker to spell out "I WISH I WAS 10" to turn him back into his regular age, just as his parents have arrived. Back at the Turner house, Vicky is back with her head still replaced by a fish's head. In the end Pops looks through the Turner's window saying "Ha! Ha! So long suckers!".