I use a cloth per kid per meal. It's usually enough to do a quick wash cycle at the end of the day.

I've tried going more than 1 meal with the same cloth, but I found they get stinky, plus if any of the kids are sick and I'm trying to keep their separate, it just seems like more of a hassle. This way I know they're never using someone else's. If/when I need to replace my current stash, I'll get a bunch of different colors to try to make it easier to keep them separate and try again.