I would put it in your contract. It gets to messy. Also they need to be washed with soap and water with those kinds of stools. It still stinks and then they get a rash because it needs to be cleaned properly. If her tummy hurts and she has the runs, she's obviously not feeling well. It's nice for mom to offer to keep her home and I would take her up on that and make sure she stays home the next day. It could be a stomach virus and you might be putting everyone else at risk by letting her stay there.