The Collaborative International Dictionary of English v.0.48:

Bopeep \Bo*peep"\, n. [Bo + peep.]
   The act of looking out suddenly, as from behind a screen, so
   as to startle some one (as by children in play), or of
   looking out and drawing suddenly back, as if frightened.
   [1913 Webster]

         I for sorrow sung,
         That such a king should play bopeep,
         And go the fools among.                  --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bopeep
    n 1: a game played with young children; you hide your face and
         suddenly reveal it as you say boo! [syn: peekaboo,
         bopeep]