I heard this in a recording of “Skip to the Loo My Darling” when I was in the third grade. Along with “Fly in the buttermilk,” I heard a verse like this:
Koss keez, what’ll I do?
Koss keez, what’ll I do?
Koss keez, what’ll I do?
Skip to the loo my darling!
And when we sang a version of the 23rd Psalm (this was before the Supreme Corut decision outlawing prayer in schools), we began, of course, with “The Lord is my shepherd”; we ended with “Koss keez, koss keez!”
Where did this strange phrase come from? And how did it get into children’s music? 
Best guess – You misheard the line “Cat’s in the cream jar” or it was a lousy recording so you could only make out “Cat’s cream.” And depeding wher eyou look, you can find the song titled “Skip to the Loo” or “Skip to My Lou.”
The line goes:
Cat’s in the cream jar,
Ooh, ooh, ooh,
Cat’s in the cream jar,
Ooh, ooh, ooh,
Cat’s in the cream jar,
Ooh, ooh, ooh,
Skip to my Lou, my darlin’.