babysitter vs playgroup

babysitter

noun
  • A person who cares for one or more babies or children for a short period of time in place of their legal guardians. 

playgroup

noun
  • An informal organised group providing care and activities for preschool children. 

  • A group of children who meet together for supervised play. 

  • A group of gamers who meet together, especially for role-playing games. 

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