Against what? How much struggle and pain are we actually seeing in the world because children have unrestricted internet access?

In an ideal world, parents would be good parents, know what their kids are up to, install parental controls on their digital devices (software solutions out there range from free/bundled to not expensive), have conversations with kids about what's on the internet and what to avoid.

Government overreach is not the answer, it's a plaster (and an excuse for more surveillance which is arguably the primary factor) over bad parenting. In the UK at least, all major ISPs and mobile providers have a basic parental/adult-content control package that is set-up by default (opt-out by the bill payer). Albeit trivial to get around with a VPN/proxy or changing DNS servers etc.

Kids will be kids as well. They'll get around restrictions, they're clever, they talk with their mates in the playground about this sort of thing. Especially teens.

I would say that normalizing giving random websites photos of yourself is harmful to children.

Think back to when you were a child. Did age verification ever stop you from doing anything? The automated, technologically-implemented age-verification is even less interested in properly verifying anything than the ID-checking bouncers at a bar. None of these things protect kids, they just annoy them and teach them that authority is stupid and lying is a convenient way to deal with stupid people.

Call your ISP and ban any NSFW/NSFL access by DNS, both in your children's phones and your home connection. Problem solved.