Rather than closing, consider advertising to fill spaces with children in the same programs as your own. That way they would be on the same schedule anyways.

You could look at your current group and either replace or decide not to take any child not able to walk or that needs a morning nap so that would eliminate two of the biggest obstacles.

This is also one of those when to tell parents things in the sense that while it is tempting to say nothing till the time actually comes you run the risk of some parents not liking their kids spending so much of the day in stroller/van and they will actually pull their kids meaning you would be left to fill spaces after the September rush for kids has happened. Telling means they may pull out early/mid summer leaving you with spaces to fill so something to consider.

Yes it is very common to do school runs but is also very common for parents to choose a caregiver that does not have to do school runs too so worth considering how the runs will effect your group.