The play was “Little Mary” (1903) with Nina Boucicault playing Moira:
CHILD (popping up). Mother, could I have just one more chocolate?
MOIRA (severely — rising).
Certainly not.
LORD CARLTON (rises). Oh, yes, let him have one. Here, Billy, catch! Catch! (Goes and flings up chocolate, which BILLY immediately puts in his mouth.)
MOIRA. You will be sick to-morrow, Billy.
CHILD (with conviction). I shall be sick to-night.