I haven't sung with kids in years, but in my experience, anything gross seems to go over well. In particular, I still hold close to my heart a series of songs set to a common military-type melody. I have no idea what this tune is called, but it's the one that the kids whistle in "The Breakfast Club." Some lyrics are:
Will make your teeth turn green
It tastes like gasoline
Will make you vomit
So get some Comet, and vomit, today!
Will make your teeth turn blue
It smells like Elmer's Glue
Will make you relax
So get some Ajax, and relax, today!
It keeps your armpits dry
It makes you smell, "Oh, my!"
Helps you get marrid
So get Arrid, and marrid, today!
Obviously, the possibilities are endless.