What to do?

Can't they sue as I have to give a months notice (not that I think anyone would bother suing over that)

Next Sept my daughter and 3 dcks will be going to school. I think this timing makes the most sense.

I would give as much notice as you can to the families, but in the end, do what is best for your family. They wouldn't hesitate to change daycares if it made sense for them, just remember that.

If it were me, I would change the contract to 2 weeks for both parties.

Businesses close all the time with no notice not even to their employees let alone customers and there is no recourse. Really other than being angry with you there is little they can do about it. From your perspective though remember that you will need to have other things lined up and may need to just take a leap of faith and determine a close date and take your chances. Your own children will need some sort of care will they not even if just before and after - if you are using the school based care those spots are filled in the spring from a waiting list so you need to be on it now. You may have before and after school time slots to fill for your own children. It isn't just about what the daycare parents will do but have you determined what you will need to do and how much notice you need to give yourself of those changes.