Daycare and preschool credentials are completely different. You could implement a preschool curriculum, but you really need to be a certified early childhood education teacher to be able to modify the curriculum as needed. Basically, a pre-made curriculum is only a starting point. You must have the educational background to be able to write your own curriculum so that you can meet the learning needs of children you are teaching, as well as a strong background in child development so that you can make proper assessments. A year-long lesson plan is written at the beginning of the year as a goal sheet, and weekly lesson plans are also written that take into consideration the strengths and weaknesses of the children, as well as their individual interests. A really good teacher will rarely have the year long match up with the weekly plans:) If I was paying for a preschool service, I would also want the teacher to be able to professionally articulate the outcomes and strategies on the curriculum, as well as their teaching and guidance philosophy.
I personally would not choose to do three sets of children by myself every day. That would be very difficult to keep up with in lesson planning, unless you were only considering having a very small group at each session, perhaps 3-4 children.
Tuition is about $120 a week for my daughter to attend a state certified, nationally accredited center. She attends 6 hours a day, 5 days a week.
So Sherry is right- without being a certified teacher your business cannot be certified as a preschool. Unless you are planning on hiring teachers that are certified, but even then you would only be able to be the business manager and not the educational director of your own preschool program. An educational director needs at least a Bachelors in the field to meet certification standards. And another point to add about the time in between sessions, is that there would not be enough time to address any concerns parents would have during drop-off/pick-up. But there are all sorts of other titles you can use if you choose to not go the route of becoming certified...you can call it a "learning center" for instance.
You also have to take into consideration that part-day and full-day preschool programs have different guidelines. In my state a part-day program has to be a three-hour session, so you will have to look up what your state requires.
Hope that helps and good luck with your endeavor!