Yes, they are. The Magic Treehouse series often takes the main characters, Jack and Annie, to different historical periods and places, like ancient Egypt or the Middle Ages. This makes them a great way for kids to learn about history in an engaging, fictional story setting.
Another option could be 'The Secret of the Treehouse Library'. This book combines historical fiction with a touch of mystery. The treehouse in this story holds a library filled with books that can transport the reader to various historical events around the world, from the Renaissance in Italy to the exploration of the New World.
The element of mystery. Many of these books have a mystery aspect to them. Maybe it's about finding a lost artifact in a historical time period or solving a mystery related to a historical event. The treehouse adds an extra layer of charm and secrecy to the whole story, making it very appealing to readers of all ages.
Among the Magic Treehouse books, 'A Good Night for Ghosts' and 'Day of the Dragon King' can be considered science fiction. They feature adventures in different times and mysterious phenomena.
I'm not sure of the exact count. It depends on various factors like recent releases and editions. You might want to check the publisher's official website or a comprehensive book database for the most accurate number.