re: apples and bananas: you cant terminate a part timer if a full timer comes along.
You could add to your contracts that part time is contingent based on the need for full time. I have in the past used this for people who only want a couple days a week, I informed them I had a spot but temp only based on the filling of the full time I had available, sometimes they bite on it. I have also approached a parent with a offer of raising fees (to near full time charge) or having them lose their spot to a full timer. Just have something in your contracts so you have the freedom to do it!
Smart idea. When my child was part time YMCA care it was based on the part time space being available. If they filled up it was understood that I could either take the full time spot of be removed from the program.