I don't want to get too off track by posting non-child spaces, but I do think it is good to recognize a spaces potential to change functions. What starts out as a playhouse may latter (when children grow up) be reclaimed as a studio space or simply a place to curl up and read a book.
Lori Marie uses her tiny little house as a place to create pretty little things. She has tons of images and more information on her site about the little house. What an inspiration!