The Collaborative International Dictionary of English v.0.48:

Playful \Play"ful\, a.
   Sportive; gamboling; frolicsome; indulging a sportive fancy;
   humorous; merry; as, a playful child; a playful writer. --
   Play"ful*ly, adv. -- Play"ful*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

playful
    adj 1: full of fun and high spirits; "playful children just let
           loose from school" [ant: serious, sober, unplayful]