Nice interview with Mary Pope Osborne, author of the Magic Treehouse books and many many others. Kids love these mystery adventures.
Did you have a treehouse when you were young?
No, but I always wanted one. I tried to write about a magic cellar, then magic whistles, then I wrote about a magic artist and studio and then a magic museum. None of those worked, and I didn't publish any of those. I was taking a walk and I saw a treehouse. It took a year to figure that out. The simplest ideas sometimes take the longest to get.