In my day home parents pay in advance and so if I had a part time family they would have the same set schedule every week and pay on Fridays for the following two weeks. What you are describing is drop in care and it comes at a higher rate then part time ( which is higher then full time) they would be giving me a schedule at least the Friday in advance as they would need to pay for those days regardless of attendance. If they need an extra day then if I have the space then ok but no switching cause I have done my planning for the schedule that was provided. You need to get tough with this family cause you are allowing them to treat you this way. Have a talk with them and set the rules out.