I have this in "The Fireside Book of Fun & Game Songs", copyright 1974, Simon & Schuster. Of the 100 or so songs, about 20 are attributed and used by permission. Sippi' is NOT one of those so I assume it's public domain.

Somewhere, I found a web site that listed public domain songs, but I can'y find my bookmark. I'll keep trying and post the URL if I find it.

...Tiger