The Magic Tree House stories — there are more than 50 of them — follow the adventures of Jack and Annie, a brother and sister whose tree house is a jumping off point for magical missions that take them around the world and traveling through time and space. For many young readers, The Magic Tree House books are their first exposure to "chapter books." They use simple language to introduce kids to literature, history and science with fanciful stories like Dinosaurs Before Dark or Abe Lincoln at Last. A companion series, the Magic Tree House Fact Trackers, provides a nonfiction version of these stories. The series has been so successful that about two years ago Osborne decided it was time to start giving back — so she began donating books to schools in need.