Mary Pope Osborne is very popular in my library because she is the author of the Magic Treehouse Books. Years ago when they were new there were several expat American families at school who introduced them to me and their friends. The problem was we couldn't buy them here in Australia so I had to wait till someone went home to America and bought some for the library. Now the early titles are readily available here and the books have built up quite a cult following. Initially I thought that Australian children wouldn't be interested in stories about the Civil War, Thanksgiving or the Wild Wild West, but the dedicated followers will read them all. The later books from Number 30 onwards which form the Merlin Series interest the children even more than the first 29. There are also Research guides accompanying the stories which are written by Mary's husband, Will or sister, Nancy. These are less popular with my children but some, such as the one on the Olympics are borrowed more frequently.
Mary Pope Osborne does write other books. In the library we have her Tales From the Odyssey, a set of six books which starts with The One-eyed Giant. They are well read because Year 2 do a unit of work where they study Greek Mythology. Year 1 look closely at Fairy Tales and in that unit's bulk loan I include her modern fairy tales Kate and the Beanstalk; The Brave Little Seamstress and Sleeping Bobby.