I have kids that age and a little older, and we have strict rules on screen time because of this. When I ask what they want to do, two will be uninterested in watching something on the TV or tablet, but if I let the other do it, they'll all watch whatever is on the screen. My kids will try to grab my phone from me randomly during the day, and if I'm doing anything on my phone or computer, they'll try to see what I'm doing. If I let them watch something on YouTube or something, they'll watch stupid, high-engagement videos (e.g. Minecraft "challenges" or whatever), and my oldest was practically addicted to a toy review channel (they weren't even interested in the toys) until I banned YouTube entirely (we let them choose how to use their allotted screen time).

There's no way I'm letting them have a phone until they can demonstrate the smallest bit of restraint. I'm considering leaving my old phone around for emergency calls, but I know the moment I let them access it, they'll get on the internet and watch random videos.

I think devices can be a fantastic learning tool, and I sometimes let them use my devices for educational reasons occasionally, but even then, they need strict limits on total time and per session time. We let them "earn" time by reading, but again, we have those strict limits so they don't binge.

When my kids can be trusted with a phone, I'm not going to let them bring it unless they have a legitimate reason to have it at school (e.g. they have an after school activity w/o a fixed end time).