The Collaborative International Dictionary of English v.0.48:

Tattling \Tat"tling\, a.
   Given to idle talk; apt to tell tales. -- Tat"tling*ly,
   adv.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tattle \Tat"tle\, v. i. [imp. & p. p. Tattled; p. pr. & vb. n.
   Tattling.] [Akin to OE. tateren, LG. tateln, D. tateren to
   stammer, and perhaps to E. titter.]
   1. To prate; to talk idly; to use many words with little
      meaning; to chat.
      [1913 Webster]

            The tattling quality of age, which is always
            narrative.                            --Dryden.
      [1913 Webster]

   2. To tell tales; to communicate secrets; to be a talebearer;
      as, a tattling girl.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tattling
    adj 1: prone to communicate confidential information [syn:
           blabbermouthed, leaky, talebearing(a),
           tattling(a)]