I dont accept non vaccinated either. I will also piont out, I agree with Lee-Bee , and will just add, it not just those other kids in your care that will be exposed. What about your family, friends that visit, and the daycare kids families. For example, I have a few family member that have newborns or are pregnant now, My home as a daycare has a higher risk of germs as is, I dont want to worry about the ones that are entirely preventable. Also, vaccinating is something I feel strong enough about that I know that working with parents with that much difference in opinion would simply not be a good fit.
Its entirely up to you, I think I would have it written in your contract that you accept kids without vaccinations, and ensure that not only are others aware, but they sign to it. In this business, you can not go too far to cover your own arse.