Eva Ibbotson's A Countess Below Stairs is sweeter than bee pollen, to quote an old Tom Cruise movie, and I mean that in a good way. If you're a mom and you've got a tween daughter who wants to start on romance novels with like-age protagonists, or if you just want to experience an old-fashioned innocent-but-touching romance, this is your book.
I myself began reading adult romances at thirteen, when my mother handed me a Jude Devereaux novel in hopes it would keep me from mourning (read: bawling) the entire fifteen-hour drive move from my best friend, and that was okay, but let's face it. Jude's got sex scenes in her, and while she does them tastefully, thirteen might not be the best age to introduce them.
Countess on the other hand, is romantic without being lustful. It was a nice breather from books with insane hormone swings and heaving hearts. The book includes simple but entirely creditable characters (with the possible exception of the main character being just a bit too selfless and optimistic, but only just a bit), which went a very long way in winning me over.
Without meaning to imply the book is in any way childish, let me just say, if you at all liked the animated film Anastasia you will really dig this novel. I'm going with a Buy on it.