Learning Languages

Language and learning are fascinating subjects. In my psychology course I learnt different theories on 'Children's ability to learn languages'. Whether children are born with the ability to percieve different sounds in their parents' language or are they able to percieve sounds in all languages. Also whether they are born with a repertiore of some sounds or is it universal to all babies born in whatever culture .Its all interesting.
On a practical scale, I have noticed in case of my own children and those of close relative's that children have really an exceptional ability to learn languages and several of them without getting confused or mixed up at all.
For insatnce, my first son, would speak Bengali at home ( because thats what we speak at home ) .He would speak Gujrati with his childminder as she is Gujrati and at Nurseries/Schools he would speak English. He would never speak Gujrati with us or Bengali with his childminder.And neither of these two at school.Also he never confused any Bengali word with Gujrati or English and vice versa.
So, basically he was learning three languages simultaneously without any problem what so ever.I have seen the same happening with all the other relative's children and believe that must be the case in all cases. I have not heard anything to suggest otherwise.