At interviews I advise my daycare families that I don't have back up care and there will be emergencies that I have to take my kids to Dr etc....
For the most part dh and I share taking days off. Recently dd#1 fractured her arm and I had to get the daycare parents to pick up their kids as I couldn't reach dh to come and get her to take to emergency- for the cast I got family to take her and bought them all lunch so I wouldn't have to take another day off on my daycare families. They understand if I take a day- I have to and I don't charge them. I would not take daycare kids with me as my focus is my kids because if I'm taking a day off, they have to be sick and they need my focus.
Our dr is out of town too ~ makes it tricky but I give as much notice as I can! One of down sides :-(