mammy vs motherling

mammy

noun
  • mamma; mother 

  • In the southern United States, a black nanny employed to look after white children; or in the antebellum South, a female slave who was close to the household and looked after the children. 

motherling

noun
  • Mother. 

  • A mother, especially a precious one. 

  • A woman's child. 

How often have the words mammy and motherling occurred in a corpus of books? (source: Google Ngram Viewer )