Doesn't directly answer your question but relevant:

https://www.waituntil8th.org/

"The Wait Until 8th pledge empowers parents to rally together to delay giving children a smartphone until at least the end of 8th grade. Let’s protect the elementary and middle school years from the distractions and the dangers of a smartphone. Banding together helps decrease the pressure to have a phone at an early age. Ten years old is the average age children get their first smartphone. You can change this!

Smartphones are distracting and potentially dangerous for children yet are widespread in elementary and middle school because of unrealistic social pressure and expectations to have one.

These devices are quickly changing childhood for children. Playing outdoors, spending time with friends, reading books and hanging out with family is happening a lot less to make room for hours of snap chatting, instagramming, and catching up on YouTube.

Parents feel powerless in this uphill battle and need community support to help delay the ever-evolving presence of the smartphone in the classroom, social arena and family dinner table. Link arms with other parents to wait until at least the end of eighth grade for a smartphone!"