I used to play this game as a kid, and the kids from my camp introduced it to me without the explanation, so I didn't really understand what was being said. I think it went something like this:

Croc-a-dilly oh my, croc croc croc!
Say cinco cinco, cinco cinco sock-a-laca
Follow! Follow! Stick your head in jello! Your face is turning yellow! 1,2,3,4,5!!

There were also other variations made by creative people, but it contains the same tune and basic meaning.

Croc-a-dilly oh my, croc croc croc!
Say cinco cinco, cinco cinco sock-a-laca!
Follow! Follow! Stick you head in Beer!
You look like Paul Revere!

Or:

Stick your head in water! You look like Harry Potter