What is the song from Captain Kangaroo that has knock knock who's there?

Bob Keeshan was Captain Kangaroo.

I had this record as a child and was searching the same as you. I recall this line.
Myra, Myra who. My Rhinosaurus is hungry do you have a bite to eat, That's who. I know it was Captain Kangaroo and Mr. Green Jeans and I used to play it on my show n tell record player. Just thought I'd answer your post so you wouldn't think you were crazy. Good luck finding it. Thanks for proving I'm not insane as well, Gabe