Parents need to know that the Magic Tree House books, written by Mary Pope Osborne, all revolve around siblings Jack ( age 8) and Annie ( 7) , who discover that a tree house in the woods near their home can transport them to different places and historical periods. The children are sent all around the globe to achieve specific goals, usually to rescue an important historical document. The books are all highly entertaining and educational. Each volume follows a certain suspenseful arc, so the children end up in at least one precarious situation, but things always turn out well. Later books in the series have a little more sophisticated language and some have more fantastical plots, for slightly older readers, but they are no more scary than the early books.