I work 6 am till 5pm for two weeks of the month and 6:30 am till 5pm the other two weeks. It is tiring but at least it is only two weeks a month. In your notification, I would say this:

Dear Parent,
Effective XXXXX, the operating hours of the daycare will be changing to XXXX. I appreciate your co-operation.
Sincerely,
Your Daycare Provider