baby boy vs lastborn

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. 

lastborn

noun
  • The youngest child of a family. 

  • The youngest member of any company or organization. 

adj
  • Born last in a family; youngest in a the family. 

  • Younger than anyone else in a group. 

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