adventure playground vs playing field

adventure playground

noun
  • A set of outdoor play equipment such as slides, monkey bars, etc., for children. 

playing field

noun
  • A field on which a game, especially a ball game, is played. 

  • Any place or context within which competitive activity takes place, such as market competition between companies. 

How often have the words adventure playground and playing field occurred in a corpus of books? (source: Google Ngram Viewer )