WordNet (r) 3.0 (2006):

man-child
    n 1: a child who is male [syn: male offspring, man-child]
         [ant: female offspring]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "manchild":
   boy, bub, bubba, buck, bud, buddy, colt, cub, fellow, fledgling,
   hobbledehoy, lad, laddie, master, muchacho, pup, puppy, schoolboy,
   sonny, sonny boy, whelp, young man, youth