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.