I am not sure why this is news. Classic economic warfare.

Parents with higher education and stable incomes have the resources, time, and knowledge to supplement their children's education. This includes tutoring, enrichment programs, monitoring social media and phone use, and advocating within schools, as well as sending their children to smaller, private schools.

Most Joe Six Pack parents hand their children unrestricted iPhones and let the schools raise and baby sit them, while the parents sit back getting fat soaking up social media and TV.

Well, it's put in a bit of a disrespectful tone, but I think you are right. Unrestricted access to a smartphone will lead to 6 hours + a day screen time. And it's all addictive junk. That can't be good.

One also sees the "educational" difference. Here a study was published concluding that poorer areas have twice the number of snackbars compared to areas with "higher educated" people. Bad food is also very cheap. It's also very easy to never read about the effects of screens on childeren and I see people with kids of ~1 sitting on the back of a bike with a smartphone blaring... Why not let the kid enjoy and learn from the surroundings? My kids loved riding a bike with me.