The Collaborative International Dictionary of English v.0.48:

boys-and-girls \boys-and-girls\ n. (Bot.)
   a Eurafrican annual (Mercurialis annua) naturalized in
   America as a weed; formerly dried for use as a purgative,
   diuretic or antisyphilitic.

   Syn: herb mercury, herbs mercury.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

boys-and-girls
    n 1: Eurafrican annual naturalized in America as a weed;
         formerly dried for use as a purgative, diuretic or
         antisyphilitic [syn: herb mercury, herbs mercury,
         boys-and-girls, Mercurialis annua]