The Collaborative International Dictionary of English v.0.48:

Youngster \Young"ster\, n.
   A young person; a youngling; a lad. [Colloq.] "He felt
   himself quite a youngster, with a long life before him." --G.
   Eliot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

youngster
    n 1: a young person of either sex; "she writes books for
         children"; "they're just kids"; "`tiddler' is a British
         term for youngster" [syn: child, kid, youngster,
         minor, shaver, nipper, small fry, tiddler,
         tike, tyke, fry, nestling]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "youngster":
   breed, brood, bud, chick, children, chit, descendants, descent,
   family, fruit, grandchildren, great-grandchildren, heirs,
   hostages to fortune, inheritors, issue, juvenile, kid, kids,
   lineage, little ones, moppet, new generation, offspring, posterity,
   progeny, rising generation, seed, sons, succession, treasures,
   youngling, younglings, youngsters, youth