Over on PsyBlog is an excellent group of articles describing 10 crucial child development studies.  This list is laden with language acquisition.  Among the list are:

  Infant Memory Works From Very Early

  How Children Learn the Earth Isn’t Flat

  Infants Imitate Others When Only Weeks Old

  When Children Begin to Simulate Other Minds

  How Infants Start the Journey to the First Word

The signficance of language in these and other classic studies highlights the signficance of language in overall development.  This is a great list!