It really all depends on what your Contract or Agreement with them says. Some providers are paid for a certain number of sick days, usually the parents are aware of them when signing on. I do not charge when I am closed, but that was my choice.

I also often don't charge when I tell parents it might not be a good idea to bring a child on a certain day. Also, just my choice. But, I do know that some providers do charge.

You have to figure out what you are comfortable with and be upfront with the parents. If you didn't have anything agreed to with the parents, I might let them have these "free" days. Then send a letter advising of your new policy in the event this happens in the future. That way everyone is on the same page. Be prepared for some backlash, some parents might get upset and others might be fine with it all.