The first reasonably "gentle joke" that came to mind for me was one used in cub scouts/boy scouts in which the "victims" are taught a new/traditional "pledge." In a dancing class it could be the chorus for the song to a "traditional" dance (that you've just created) from an unspecified culture(?). Body movements (dance steps?) that place the participant in at least mildly awkward positions are a common accompaniment

The pledge is:

"oWAH taGOO siAM" (repeated until someone catches on and translates it for the rest of them)

There is the danger that some of your kids may have heard of it since it is an "oldie," but often those "in the know" will keep quiet until a "new learner" blasts it out.

There are some other variations on the "pledge," but the ones used for Frat initiations were mostly too crude to be worth remembering.

John