What every baby knows reflection

It is pretty interesting to learn that over the last thirty years we have learned more about babies and young children than in the entire history of  mankind. The author mentions that babies and young children have fairly complex ideas about the way the world works and they are changing and devoloping and testing these ideas from birth, I'd like to know if these theories change or develope faster due to the ethnicity, environment or upbringing of the child. Or if all childrens mind are programmed with the same theories and eventually change as they are introduced to varying environments. I also want to know how they tesy tested the brain capacity of very young children since it must be hard to get the cooperation of someone who can't comprehend what you are doing or what they should be doing. The example I thought was incredible wass that after being born forty five minutes earlier the new born child could interpret the expressions on a grown mans face and recognize that they too could produce these images onto their own faces. They had never seen a mirror, so how did they know that the man above them was doing something they themselves could do? That is what the scientists are trying to figure out.