Quote Originally Posted by paulb
The point about first language acquisition is that it is done fairly quickly without (normally) relying on teaching grammar. By the time a child turns four he has mastered the majority of the grammar he will ever learn. I have a four year old son who speaks nearly flawless English within his vocabulary limits. Since he didn't really talk for the first year, that amounts to just three years of active language learning.
Toddlers learn grammar ( not just separate words ) of their native language long before they begin to speak. Google for "head turn preference". And when they become older, they lose the ability to learn that fast ( e.g. distinguish sounds that are allophonic in their first language )
Just a link.
http://www.pediatricservices.com/parents/pc-34.htm