This is a short TED talk by Patricia Kuhl, co-director of the Institute for Brain and Learning Sciences at the University of Washington, who talks about how babies learn one language over another, that is, by listening to the people around them and "taking statistics" on the sounds they need to know. Clever lab experiments (and brain scans) show how 6-month-old babies use sophisticated reasoning to understand their world.
The critical period to learn a language is between 0 and 7 years of age. Patricia Kuhl talks about this critical period and investigates the brain process during this time.
Remember you can activate the English subtitles to fully understand the talk.
H/T to A Clil to Climb.