If I can manage it with the current amount of children I have and I don't feel that it's putting the remainder of the children in danger (contagious) and if the child does not need immediate medical care then I will simply let the parent know, but also let them know that the child does not need to be picked up.
I find most parents want to pick up their child if they're ill.
For a few watery poops, unless the child needs to be bathed or the poops are not being contained in a diaper, I'd let the client know, but keep the child.
I think sick policies are great, but when it comes down to it, it's a judgement call.
It depends on the day, the time, what's happened, is there a fever, is the child cranky, is there something the child needs that we can't provide (Tylenol, bath ect. )
But, I always advise the client of what's happening and let them choose the course of action unless I feel the child needs to leave. Then I just call them and tell them "little johnny has been sick and needs to be picked up. What time can I expect you, the sooner the better"