I was going to clarify what Sunny said... There is a difference between diarreah (specific texture and appearance, as well as being gawdawful smelly) and loose stool (which could be teething, diet or stress).
If it's honest to goodness diarreah, then twice is once too many times for me. They get to go home if it happens more than one time while with me in a day. Yuck.