I don't take school age children because to me, a space is a space and with the limits in place, it makes no sense to allocate a space to a child who is going to pay a reduced fee for fewer hours.

If I did decide to take on this, I would :-

1) decide if I'm even going to offer full day care. The school based programs here only open if the school is open and there's no care for school holidays/closure days. Clearly those parents manage to find alternative cover and so there are options out there for this. I think for me, the advantage of taking school age children would be the reduction in hours that would allow me to do other things during the day time and so I might not even offer the option of all day care.
2) if I was going to offer care when school closed, I wouldn't charge monthly. I would have a daily rate for term time and a different rate for full day care. Then every two weeks, I'd be paid in advance where I'd be able to see from the school calendar what fees would be due for the next two weeks. I wouldn't try and figure out an average so that the fees were always the same.