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:

Comet

Will make your teeth turn green

Comet

It tastes like gasoline

Comet

Will make you vomit

So get some Comet, and vomit, today!

Ajax

Will make your teeth turn blue

Ajax

It smells like Elmer's Glue

Ajax

Will make you relax

So get some Ajax, and relax, today!

Arrid

It keeps your armpits dry

Arrid

It makes you smell, "Oh, my!"

Arrid

Helps you get marrid

So get Arrid, and marrid, today!

Obviously, the possibilities are endless.