i'm looking forward to seeing the answers to your question - we have a place in wells - and will be there for two weeks later this month. what i can think of is the movie theater. i guess it depends on how hard its raining. you can walk around downtown kennebunk or perkins cover in a drizzle or visit all the antique stores on rte 1. you could have a big lobster lunch - or go to the Maine diner, check out Old Orchard, go to the outlets in Kittery. there's a trolley museum, a lighthouse musuem and a car museum nearby. some of the mini golf places have indoor arcades. bring puzzles and games and dvds just in case. on rte 9A there's a playground - it's pretty big. keep an eye out for churches that are having pancake breakfasts and bingo nights. if you don't mind, let me know if you hear anything different. thanks.
anyway, stay positive - maybe it won't rain at all : ) and have a great vacation!