Both of my sons have now attended AppleTree Preschool (Rt. 59 and Fraser). They do have a lottery process that will take place in January for next years class. It's a small program, very loving and great for the kids. They work with the kids at their pace and aim to give them the skills that are requested for starting K in the plainfield School district.
http://www.appletreepreschool.org/
They have all the lottery information on there. But once you are an AppleTree mom, always an AppleTree mom. And your (even future) children will get preference.
C.