Word:

  changeling

1. changeling (n)
  a child secretly exchanged for another in infancy.

2. changeling (n)
  a person of subnormal intelligence.

Words derived from changeling
check,  delay,  retard

changeling is an instance of
child,  fry,  kid,  minor,  nestling,  nipper,  shaver,  small fry,  tiddler,  tike,  tyke,  youngster,  simple,  simpleton

Word and things that fall within changeling
mongoloid