Boris e Rufus (Monster, Muscle Growth, and Age Progression Transformations)

Boris e Rufus is a Brazilian cartoon. In episode 20, "A Fonte da Juventude" (The Fountain of Youth), the protagonists journey to an underground land inhabited by Germanic piglets who have never grown up. The pigs concoct an aging potion that has unexpected effects...

There's also a very quick reversion scene.

In episode 3, "Cilada!" (Trapped!), the protagonists are visited by Nino the cat, who needs help to counteract the side effects of a scientific experiment...



There's another transformation at 06:43 -- reversions are at 6:03 and 08:30