I began to learn Chinese from my early life. My baby sitters in were of Chinese decent. They did not know English so they spoke to me in Chinese. Just like how many children with Hispanic care takers learn Spanish.
I learned and practiced Chinese with them my whole childhood even though I didn't want to. It was not until later on I did not see the possibilities available to me in both government and the private sector with this language ability. Though my accent will always be a foreign accent in Mandarin, I am able to understand the concepts of the language very easily.
My early introduction to Chinese has made it easy for me to learn other languages on a basic level. My Spanish is decent and from Jiu Jitsu and my Brazilian friends I know a little Portuguese as well.
I really recommend that people encourage their children to really understand another language, it not only will enrich a child's 1st language vocabulary but studies show that fluency in another language will decrease the likelihood of Alzheimer's later in life.