Child safety features are not going to solve this problem. All it takes is one parent giving their kid a phone with an adult account and all that progress is undone. I am convinced it is going to take a cultural shift for any positive change to occur - self-policing and, if necessary, social stigma.
This kind of behavior of giving young children phones will have to be outmoded in a generation or two. Until then, there is going to be a lot of growing pains.