The MAGIC TREE HOUSE FACT TRACKERS is a bestselling series of nonfiction books that expand on the Magic Tree House fiction, and are written by Mary Pope Osborne together with either her husband Will Osborne and her sister Natalie Pope Boyce.These books break complex subjects down into simple concepts that young children can readily comprehend. They help develop a child’s skills at reaching conclusions through the logic of cause and effect. But the most fundamental gain of the nonfiction Fact Trackers is that they give children an appreciation for the wonders of the “real” world and inspire a curiosity for learning more about history and natural science.