Time to be firm. Tell them that they pay for a spot in your daycare. Let them know that you will be applying the child's absence to their holiday time or they can pay for the week today. This is your income!
One of my clients tried this a couple of years ago. They put their child in half day camp and brought him for half day afterwards. They thought that they just had to pay for my half day fee. Nope, full day and they paid. Would this work in center care? No.