Honestly, the best case scenario is to let things run their course. The kids would say meep a lot for a few minutes, and then it would get boring and they'd stop. But you turn it into a big deal? Weeeeelllll now, you've stirred up the young ideologues! "This is some fascist shit, man!" And now they will put their energies into something actually disruptive: tempest-in-a-teapot clamors over free speech.
And not to say that it won't be justified, in some ways. Just let kids be silly every now and then as long as nobody and nothing gets hurt. Pranks are old as time. #meep