The Collaborative International Dictionary of English v.0.48:

Moppet \Mop"pet\, n. [From 3d Mop.]
   1. A rag baby; a puppet made of cloth; hence, also, in
      fondness, a little girl, or a woman.
      [1913 Webster]

   2. (Zool.) A long-haired pet dog.
      [1913 Webster] Mopsey

WordNet (r) 3.0 (2006):

moppet
    n 1: a little girl (usually one you are fond of)