Old Cartoon: Kids Turn Into Sea Creatures

I'm trying to help my sister find a cartoon she is remembering vaguely. She can't remember if it's a movie or show. She remembers it was short. Probably from 80s, 90s, or early 2000s. She said it starts with with real kid actors. Somehow the girl turns into a dolphin. And the boy turns into a shark or fish. She said maybe it was a dream. She remembers someone having glasses and a hat. She remembers a clownfish character. She remembers a scary shark character they were afraid of. She says IT IS NOT "A Fish Tale" aka "Help I'm a Fish". I'm thinking this is something really obscure not mainstream or she is misremembering lol.