What I probably would tell the mom that wants to change her hours is that you are unable to do it because of the loss in income explaining that what they are booking is one of your five spaces in your daycare and how many hours they attend is irrelevant. I would likely give them care from now till January and advertise for new full time kids for January. If mom does change her hours but agrees to the full time fee do not belive that she will stay. She will be looking for something cheaper and will jump ship as soon as she finds it so better to just hang onto them at whatever they will pay till you can fill the spaces yourself.

If you take kindergarten kids and your area has half day school you might have the option of getting someone needing care in the morning but not the afternoon but unlikely at this point in the year and you really don't want the lunchtime switchover every day.