number of copies. more than 100 million copies worldwide. they've been translated into 32 languages. the magic tree house series is written by mary pope ozborne, and on tonight's rock center with brian williams, nbc's meredith vieira explores how she captures the imagination of children the world over, like 9-year-old erin brullard. >> sounds like she means a lot to you. >> uh-huh. i really like the books. >> you heard it right. books. it wasn't a pop star or even a movie star who inspired this homeless third grader. it was an author. her name is mary pope ozborne, and her magic tree house chapter books are so wildly popular among 6 to 10-year-olds that as far as they're concerned, she is a rock star. [ chanting mary ] >> you are a rock star. >> their enthusiasm comes gushing out in fan letters. that one aaron wrote is just one