The fetus brain cell start build when they were 3-4 months in the mother womb, and then after they born until 3-4 months old the brain cell will growth faster reach up to billions of cell. However, there is not connection yet amongst cells.

It will start when fetus step into 6 months old, and here is the time when connection started amongst cells. Therefore, brain will build their function series. The quality and complexity of the relation series amongst brain cells are determine by stimulation that children get.