child's play vs picnic

child's play

noun
  • Something particularly simple or easy. 

  • Used other than figuratively or idiomatically: the play of a child. 

picnic

noun
  • An easy or pleasant task. 

  • An informal social gathering, usually in a natural outdoor setting, to which the participants bring their own food and drink. 

  • The meal eaten at such a gathering. 

  • A cut of pork from the shoulder area (above the front leg) of a pig. 

verb
  • To take part in a picnic. 

How often have the words child's play and picnic occurred in a corpus of books? (source: Google Ngram Viewer )