A VPN can't get around a cigarette and alcohol ban.

Perhaps children should be given locked down phones, with fines for parents who buy non child safe phones for their kids. It would take time for this to take effect but a social media ban would actually be effective at the end.

The harm hasn't been adequately demonstrated though. Whereas we know cigarettes are harmful to everyone.

Alcohol in the UK can be consumed in the house from 5 years old. Which is the point. That societal norms at work. Everyone knows it's not ok to let your young kids get drunk, but we trust society to let parents decide what is appropriate and when.