Sorry to hear that your son/daughter has been so ill.
I hope things are on the upswing.

Without knowing ANYTHING else about this situation, it doesn't seem very fair. But, what reason were you given? They must have said something about why you were being let go? It is rare that an issue comes up, out of "nowhere". Chances are, something has mitigated this decision.
As to whether it's allowable for your provider to do this, I would have to see your contract. I don't think I would feel right about it, though.