Is it ok to let baby to fall down for them to learn? Will it hurt their brain? As I don't wish my kids too protective also. My baby 8months now. I bought a thick carpet for her (2inch). She always unaware and fall behind while sitting.

Young children are not as fragile as they look and they are quite resilient. It would take a lot to permanently affect them. I feel that experience is the best teacher and unless it is a life threatening situation, parents shouldn't be too over overprotective. But that's my 2 cents anyways.