Say you were a guardian or parent and get to decide when a child can get a phone or use a computer and get internet with it. If you wish you can also install software and change router settings to what you see fit.
Some parents decide to forbid the internet completely, others are more relaxed. Some go the helicopter route, and some do not care whatsoever what their kid does online.
What is your policy on letting a child use the internet?
Even so, less is better. Being exposed X hours per week through friends is still better than giving them direct access to a dopamine drip feed for 56+ hours per week (avg for teens in 2025). If they really want it, you can set limited access via a home desktop/tablet and teach the same digital literacy.
A kid doesn’t need a smart phone in the same way that they don’t need their own car. They don’t need to go far distances with bulky items and passengers; they don’t need pocket access to banking apps and Slack. A dumb phone/watch can keep them in contact with anyone they could possibly need to talk to.