http://www.campmaine.com/home.php
Are you looking for actual camping, or campground camping?
If you've got kids, stick near Old Orchard, Saco, Kennebunk area where you'd be near the beach. There are also a lot of museums in southern maine. That website will be a lot of help for you as far as attractions in the area.
This is a nice campground in Old Orchard--http://www.gocamping.com/Pages/oobcamphome.htm
Good luck, and have fun!