How long will it take for hair to grow

My baby niece (I am raising) is going to be 2 years old next week and still has very thin blondish hair that only falls at her neck. She also has the "baby" mosaic still (hair that seems to grow from a circle at the center of her head.) I want to grow her bangs out and they refuse to do anything but lay on her forehead, also how long does it usually take to get their hair to grow. I have only cut it once and it was just to even up some scraglys on her neck, as well as trimmed her bangs from time to time. My whole family has had thick dark brown hair practically from birth so I just don't get it. any advice would be appreciated.