IKR is "I know, right," Pam.
As far as I know, the books your sim has written aren't available for purchase. I've tried this and unless my game is bugged, it's not possible to purchase books that were written by one of your household sims.
An adult sim can read any book to a child sim once the book is off the book shelf. Children's books are shorter, however, and therefore more quickly read. Children can read books in any genre, just like adults can.