>>304860050
It is their responsibility, but most parents are tech illiterate and just see it as a video game/toy. 
>it's not like literal kids are going to instinctively avoid it
They might if they enter their age and get a message saying it's restricting features for them. I made my first xbox account when I was 13 and was honest about my age and it told me I would have limited features because I'm underage. I immediately made a new one and lied to say I was 18.