little girls' room vs thunderbox

little girls' room

noun
  • Synonym of ladies' room: a public lavatory intended for use by women. 

  • A room belonging to or used by little girls, particularly their bedroom. 

thunderbox

noun
  • Any lavatory or toilet, especially a rudimentary outdoor latrine or toilet, or an outhouse. 

  • A box of metal balls which is shaken to create a thunder sound effect. 

  • A chamber pot enclosed in a box; a portable commode. 

How often have the words little girls' room and thunderbox occurred in a corpus of books? (source: Google Ngram Viewer )