The Collaborative International Dictionary of English v.0.48:

Prattler \Prat"tler\, n.
   One who prattles. --Herbert.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prattler
    n 1: someone who speaks in a childish way

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "prattler":
   agreeable rattle, babbler, big talker, blab, blabber, blabberer,
   blabbermouth, blatherer, chatterbox, chatterer, gabber, gabbler,
   gasbag, gibble-gabbler, great talker, hot-air artist,
   idle chatterer, jabberer, jay, magpie, moulin a paroles, patterer,
   prater, rattle, windbag, windjammer, word-slinger