Creature of the Night by Kate Thompson

Bobby is fourteen and thinks he is a pretty tough criminal. He started stealing cars and other valuables with some of his Dublin mates when he was eleven years old. When his mother decides that Bobby and his little brother, Dennis, are moving with her to a little village in County Clare, Bobby has no intention of staying there. He will get back to Dublin however it takes.

Bobby had no idea that something about the little house they move into would change his life. He and his mother almost laugh when an old woman who lives nearby tells them that they must put out a bowl of milk for the fairies every night. But things get very strange. Soon Bobby's mother is just as eager to get back to Dublin as Bobby... if it were only that simple.