baby boy vs baby of the family

baby boy

noun
  • A very young male human being, from birth to a couple of years old. 

  • A term of endearment for a man. 

  • A man who is immature or infantile. 

baby of the family

noun
  • The youngest member of an immediate family. 

  • A member of an immediate family who behaves as, or is treated as though they were the youngest member of a family. 

  • An adult member of an immediate family who is treated by others in the family, especially the parents, as though they were a child. 

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