Guest

Everyone knows you don't compliment a baby.  In fact, the more attractive and pleasant the baby, the more you should insult him.  This is a protection against the fairies.  If a fairy overhears you praising a baby, she might steal him and replace him with a changeling.

Mollie momentarily forgets this one day while she is watching her baby brother while gardening.  She looks away for a moment, and when she looks back, Thomas has been replaced by a changeling.

Her only hope of getting her brother back is to journey to the land of the fairies and demand an exchange.  Her family has been calling the changeling Guest, but he screams and bites constantly.  As she continues on her journey Guest grows faster than a human child, and after a chance encounter with a peddler on the road, he begins to talk.  She soon realizes Guest is no longer the angry changeling.  He's just a child who is terrified to return to the land of the fairies.

The fair folk know Mollie is coming, and they have plenty of traps and tricks to keep her out of their realm, but Mollie refuses to give up no matter what dangers she faces.

Mary Downing Hahn's newest book is a dark fantasy with the perfect amount of scary for middle grade readers.  Recommended.