> If I ever have kids, I'll make a concerted effort with other parents to prevent them from joining any social media before they turn 16

Honestly that seems unlikely. If all their friends are on some platform they will find a way to be on it also. Best you can do is really try to educate them on how badly things can boomerang and that the internet never forgets. But even at 16, most kids don't have the life experience and perspective to really understand this.