My nephew was riding with his mom at around 6 until he tripped getting off at home and burned his leg on the exhaust (his dad threw a fit). I wouldn't ride with a kid in Fayetteville or any larger town with lots of traffic but quiet small towns or smooth country backroads I would take my own kids.
I recently saw a woman riding a scooter with a 7 or 8 year old girl in her lap. Neither of them was wearing a helmet or any other riding gear as they rode through downtown traffic in New Britain, CT (this is a city, FYI) . They did this while passing a cop directing traffic with no consequence.
There is no helmet law in CT for motorcycles or scooters, meanwhile if that kid were riding her bicycle down the street without a helmet she would be in violation of the bicycle helmet law.
As a parent myself, I try to never judge any other parent. I am sure this woman loves her daughter. I don't know if that was this woman's only mode of transportation and where they were going was a life or death situation. I do know that the little girl I saw was in danger, and at minimum could use some gear to keep her brain safe and her skin off the pavement. I hope that they don't learn the lesson the hard way.
RIP to the deceased, and I hope their families can find peace with what has happened.