For myself it is 3, if they get sent home they can't come back the next day. If the following day they come back and have another runny poop they get sent home after the first one as whatever is going on is still present.

We had something go through my daycare. It seemed to hit the kids differently though. 3 had more vomiting than diarrhea. My daughter got diarrhea and I ended up with the diarrhea too. I had it for 11 fricken days!!!!! I was about to go to the doctor and just like that it was over. 11 days though! It was ridiculous. It wasn't constantly though and other than that I felt totally fine. My daycare parents all seemed to get the same thing as well. My sister had it for 9 days as well. I am so glad it seems to have run its course here! Knock on wood.