I only take full-time children because part-time mean lost income if unable to find family wanting opposite day. Yes it mean sometimes a full place empty for longer but still less loss that endlessly have half space unused indefinitely. I bent own rule about 2 year ago and took 4 day a week child who go grandparent on Wednesday and it took 18 months to find someone wanting that empty Wednesday - 52 week plus 26 week = 78 week of lost Wednesday money which equate to 15.5 full weeks. It would not likely have taken me 15 week to find a Monday to Friday child had I declined.

In your situation I think first option is that parent have pay full week. That would be preference. If that not being taken up in your area, then maybe contact for fixed days when child not in school and no contact for care on opposite days when they are in school. If school closed on their day when no care contacted, that not your problem.

So child who go school Mon, Wed, and Fri would have contract with you for child care on Tue and Thu only. If school is out on Monday, then that parent issue as that not contracted day with you. They can reach out and see if you have availability but if not, you not obligated to fix their school schedule issues.