Unless dh is a partner in your business, do what your contract says and what's best for all, you get to call the shots. And yes, my contract says payment is for enrollment, not attendance. It doesn't matter where a child contracts any sickness because just think of all the gray areas and manipulation by dcps that can cause.
I would exclude as soon as it's been diagnosed or you have a strong feeling of what it is, until most of the blisters have scabbed over. Trouble is they're already contagious by the time that happens and for a good amount of time afterwards. But often, that's the same with any sickness/disease. You can only do what you can do.