I know that it's easy to access but but actually VPNs are a bit of a ballache. And it depends how it's implemented. If your age is logged to your account then Snapchat (my personal bugbear) can be disabled from the phone. So then they have to find an unlocked device, or a computer, get an overnight 16baccout , log onto it or use a VPN. So all of this makes it much more difficult.

You will never stop anything 100% but this isn't simply accessing a porn site with a VPN. These are embedded into the devices that are with them all day and there are different ways to reduce the harm.