I think a huge part of the problem is that car companies aren't properly incentivized to protect pedestrians. It's easier and cheaper to prevent my car from hitting something that can damage it than to prevent my car from hitting something that it can damage (easier to detect buildings and other cars than to detect children). If you were the CEO of a car company and had a finite amount of money to spend on research on driver assist features would you rather spend it on the easy problem of protecting your customers or the expensive problem of protecting other people? Furthermore, as a consumer, would you rather buy a car that costs x dollars that protects you or costs x+y that protects other people?