How does a baby learn language, when learning requires concentration

[penguinsare@xxxxxxxxx (Penguins Are)]

I still didn't get an answer that makes any sense to me.  


Concentration is required to memorize-focus.  Then how does the baby
learn words and basic grammer by age three when they are too young to
focus narrowly?  

How do they get all the words when adults studying  a foreign language
must go over and over vocabulary lists to remember anything?  

This seems to me a reasonable question.  It's not to play with the list,
as some insulting person wrote when I posted it before, and nobody is
selling anything.