The Magic Tree House series is great for both reluctant and avid readers alike! The exciting adventures and engaging historical facts make the books both fun and educational. For those who are not familiar with the Magic Tree House series, Jack and Annie are friends who come across a tree house that can travel around the world and through time. Each book covers a different educational subject, like dinosaurs, mummies or the revolutionary war, in a magical adventure that children love.
The original Magic Tree House books are numbered #1-28, and the longer books intended for more advanced readers are “Merlin Missions” and originally started as book #29 but were later given their own number system as well as new cover artwork. Which is why sometimes you will see books referred to as number #30 otherwise as Merlin Mission #2.
Later, Mary Pope Osborne and other supporting authors, wrote non-fiction companion books called Magic Tree House Research Guides, (later renamed the Magic Tree House Fact Finders) which go into more depth on the subjects covered within the books. The research guides are meant to be paired with specific books and work well for homeschooling supplements.
I would recommend these to read out-loud to children as young as 5, and the new Merlin Mission books are recommended for children as old as 10, making it a great series everyone in the family can enjoy. For more information on the order of the series or which Research Guides pair with each book I recommend the chart at the bottom of this Wikipedia page.