Please Help Me!!!!! ?

I'm babysitting 3 children ages 13, 7 and 3. The 3 year old is still in diapers and I believe she has the runs (aka diarrhea). She has already smacked her brother with a broom and is freaking out because I won't let her go back down stairs with them. I can't get a hold of their parents WHAT DO I DO? What can I give her to stop the diarrhea? They're parents aren't coming home until tomorrow sometime, I have no idea when!!!!!