This song is 'The Beautiful Briny' from the Disney movie Bedknobs and Broomsticks. It was written by Roger and Richard Sherman and was meant to be used in the movie Mary Poppins. There was no room however and the song was placed in Bedknobs and Broomsticks.
A great song from an underrated movie!
Interestingly enough, this song helped to inspire "Under the Sea" from the Little Mermaid!