I totally understand your point and others commenting here. IMHO the main problem are other parents giving their children their "old" phone because they want the latest one.

There is a finite amount of control that you can have, there's always a friend with another phone where they can watch everything.

Communication is the key, we talk a lot with our 11 yo about the danger and pitfalls of social media, electronic games etc. Yes, he has a simple smartwatch (bare minimum: call, location), yet I think we managed to develop a healthy digital hygiene. I wish you best luck!