Sentence:  His nurse had told him all about <WSD>changelings</WSD>, and how the little people would always try to steal a beautiful human child out of its cradle and put in its stead one of their own ailing, puking brats ... 
Meaning of the word marked with <WSD> tags:  In pre-modern European mythology, an infant that was secretly exchanged for a mother's own baby by an evil creature. (In British, Irish and Scandinavian mythology the exchanged infants were thought to be those of fairies, sprites or trolls; in other places, they were ascribed to witches, devils, or demons.)