I actually wouldn't recommend reading Magic Tree House out of order. While each of the books are completely understandable on their own, they also build on each other, so reading one that comes later will actually create spoilers for earlier books in the series.
I actually wouldn't recommend reading Magic Tree House out of order. While each of the books are completely understandable on their own, they also build on each other, so reading one that comes later will actually create spoilers for earlier books in the series.