Phineas And Ferb: Season 3, Episode 46

3 - 46:

Phineas and Ferb are turned into babies by Doofenshmirtz's Babe-inator, but the crazed doctor soon decides to give up his evil ways and join Perry as an agent for good. Elsewhere, the guys create a colorful fall world; Doofenshmirtz mentors a student.