I personally would not do it unless they paid for a full time spot. I made the mistake and did this with a family. I hated their schedule being all over the place, they kept changing days last minute, it was a royal pain in the butt! I changed their minimum 3 days a week to a set 3 days. Once they made changes I charged them for their original days plus the new ones. It wasn't too long until they stuck to their first schedule and shortly after that they left. Now full time only and I won't look back - no exceptions !!