For those that don't want a playhouse in their yard why not create a nest for the kids. This way you have a place for children to play and a unique piece of garden art that you get to design and create.
the Bean House. a primitive frame, covered with chicken wire. Scarlet Runner Beans growing on it. Scarlet Runners are a delicious french green bean, whose vines grow up to 20 feet long! They also boast a beautiful scarlet bloom that attracts hummingbirds.
You can build a tree house in your back yard as an office or extra room, or guest house or if you really love your kids a play house for them. But I am not so sure you want to waste this kind of awesomeness on kids.