The Angry Beavers (1997)

S3E18 Act Your Age

When a massive ancient tree crashes onto the Beavers' home, Dagget and Norbert begin to squabble over who gets to take the first bite. However, after they each take a bite, they magically transform into their younger selves! Faced with a lack of food in the house, Lil' Dag and Lil' Norb set their sights on the fallen tree's prized golden acorn as their next target.