"The Magic Treehouse" series is great and there are a lot of books available. Not only is it about magic and fantasy, but each book incorporates historical figures and places into it, so it's a bit of a history lesson as well. Another plus, one of the main protagonists is a young girl (it's a brother and sister team), so she may relate to it. My son read most of them between 1'st and 3'rd grade, he's an advanced reader, in the middle of "The Invisible Man" now. TMT is great for young readers (it really boosted his interest in reading).