LANGUAGE

I marvel at my grandchildren's speed in learning and mastering the English language! 

I read something about that in Keep Your Brain Young, by Guy McKhann (M.D.) and his wife, Marilyn Albert (Ph.D.):

Our inborn brain mechanisms for learning language reside in areas of the brain that two nineteenth-century physicians first found, and we use these areas to acquire language until we are 10 or 12 years old.  After that, to learn a new language, we use different brain mechanisms.  The parts of the brain we use when we learn a language later in life include not only the original language systems, but other parts as well.  It is as if we no longer process language as a special function, but now use the same brain mechanisms to learn it that we use for learning many other things.  That explains why a child younger than age 10 learns a language so much more quickly and completely than an adult.  The child is still using the brain areas dedicated to acquiring early language - specific mechanisms we don't tap into when we are older.  (pp.128-9)

My grand-daughter, Rylie, watches Dora cartoons.  As a result, she knows the color red as rojo.  Her early language mechanisms are picking up snippets from this cartoon and incorporating them into her understanding! 

Logic says if you want a child to be bi-lingual, help them learn those languages before the age of 10.