I charge teachers a higher rate during the school year and then they have the option to bring their child one day a week during the summer. Here is what it says in my contract. Only ever had one teacher actually do it but she understood why I was doing it. It was to prevent what had happened to me by the friend (fellow teacher) that had referred her to me in that she had said oh yes child would stay for the summer then come June changed her mind and of course wanted care again in Sept. Ok so it didn't copy and paste correctly spaced but you get the idea. It does look a lot neater on my fee handout page.

September-June Care $225.00 all ages (5 days per week, maximum 10 hrs per day)
(Teachers – weekly) Applies to school year including school breaks and PD days.
During the summer, child may come for one day of care per
week (day of my choice). Additional days will be regular $40 fee.
Space will be held over the summer with a non-refundable retainer fee, paid in June, which is equal to two weeks of care ($450). Fee will be applied to the first two weeks of care for the following September.