And they would, I think, be peaceable assembly protected by the First Amendment, even in a time of epidemic.
From the County’s page:
Q: Are car parades, cruises, and joyriding prohibited?
A: No, they are NOT prohibited by any stay at home order issued by the Osage County Health Department. In addition, according to guidance issued by the Adjutant General, the Governor’s stay at home order does not prohibit “joyriding, cruising or parades” so long as the “occupants of the vehicle reside in the same residence and vehicles do not stop and congregate.”
The Kansas Justice Institute / Kansas Policy Institute helped bring that about, and it does seem to me that a total ban on parades, including car parades, would likely be unconstitutional: It wouldn’t leave open any alternative channels for public assembly, and it wouldn’t be necessary to serve a compelling government interest (given that people driving in cars with closed windows seem quite unlikely to infect each other).
Of course, some content-neutral regulations would still be permitted, for instance to keep the slow-moving parade from tying up traffic during rush hour; but that’s generally true of any large parade that risks tying up traffic.