The Collaborative International Dictionary of English v.0.48:

Foundling \Found"ling\, n. [OE. foundling, fundling; finden to
   find + -ling; cf. f["u]ndling, findling. See Find, v. t.,
   and -ling.]
   A deserted or exposed infant; a child found without a parent
   or owner.
   [1913 Webster]

   Foundling hospital, a hospital for foundlings.
      [1913 Webster]

WordNet (r) 3.0 (2006):

foundling
    n 1: a child who has been abandoned and whose parents are
         unknown [syn: foundling, abandoned infant]