If you're starting a preschool named Willow House it can't hurt to have an actual willow house, right? Kristin (who keeps the wonderful blog Kleas) is doing just that and her family made this terrific play structure in an afternoon. If you have a few feet of land and can get your hands on some willow her photos show you how easy it is to make.
A willow house is very simple and can play any role in kids' play that they can imagine (house, fort, wigman, igloo, etc.) or just be a shady reading spot on a hot day. Kristin was lucky enough to get her willow from a friend. Who knows, someone you know may have it growing on their property. Or you can check with local nurseries to see if they sell it.
See Kristin's photos of the willow house construction process on her blog Kleas. (Good luck with Willow House!)