Russian Federation is widely expected to conduct its annual military parade on May 9th. The parade traditionally takes places on the Red Square with many "military units" marching over a prolonged period of time. There is little, if any, room around the parading military that is taken up by civilians.
While it would be an act of war for another country to bomb those military units, would it be a war "crime?" Are marching military units, most of which look like showmen rather than actual soldiers, considered military? Or are they civilians despite the uniforms?
Edit (May 11th, 2023):
It's almost funny how well this question has aged.
It's a year later, and there are now media reports that Russia's 2023 "Victory Day" parade has been significantly scaled down precisely because of the security concerns about possible drone attacks by Ukraine.
The question is as relevant now as it was back when I first asked it.
This question is particularly relevant to this war because so much of it revolves around cat-n-mouse hunting of opposing military's units by both sides. And, of course, thousands of troops on display, concentrated in one place, would make for an easy target.
So the question of whether such an attack would violate the laws of war is more relevant than ever.