Don's Fountain of Youth (1953) on Netflix

While traveling with his nephews, Donald stops at the "fountain of youth" and tricks the kids into thinking he is a baby again. However, he gets tangled up with an aggressive mother alligator and her babies.

The boys are more interested in their comic book than the sights on their Florida vacation. When the car breaks down next to the spring "mistaken for the fountain of youth", Donald decides to have some fun with his nephews and hides the part of the sign saying "mistaken for". As baby Donald, he starts shredding their comic book and generally acting like a spoiled brat. But when he decides to pretend he's turned into an egg (borrowed from an alligator), he's in for trouble he hadn't bargained for once the gator finds out.

—Jon Reeves <jreeves@imdb.com>

While traveling with his nephews, Donald is disgusted that they are only interested in comics. He stops at the "fountain of youth" and tricks the kids into thinking he is a baby again. However, he gets tangled up with an aggressive mother alligator and her babies, and makes a hurried exit with the nephews.