Happy Friday everyone . I need some advice.

I have a soon to be 3 year old, whom I've been watching for 2 years now. Her mom has a steady full-time job and the father started working in construction last spring. She has come to daycare mostly everyday. Her attendance started dropping in fall. She stays home with dad when he is not working, due to the weather.

Because of the great winter we have had and having she has barely been at daycare. Just to give you an idea:
January - 10 days
February - 8 days
March - 5 days.

It didn't bother me too much in the beginning. It is only mom working and they save on the daycare expense. She even has an evening job. But now it is starting to bother me. I am worried because of a) the bill that could be passed b) today I only have 1 child present and c) I am at a loss because she only pays for the days she is here.

What can I do, that is fair for me. I have this unbalanced spot now, but come the good weather I know she will be here everyday. She is a good child and parents a pretty good (mom does have a mouth on her though).

I need a plan that would work in general for all parents who have jobs like this one. Something that I could include in my handbook too so that it is fair for me and fair for the parents. I don't like to charge a parent when I haven't worked for a day, but I am really loosing with this situation.

HELP