> but it wasn't their responsibility to prevent children from looking at their magazines

They weren't made to guarantee no child could peek at them, no, but they do have age restrictions that are followed (a child who picks one up couldn't buy it) and they were often on the top shelf. The kind of thing a basic risk assessment would flag "hey we keep the hardcore porn in front of the pokemon magazines...".

> The videos are split up into packets, and transmitted through an ad hoc chain of servers until it arrives, via their ISP, on their computer. The web sites are the equivalent of the publishers, and ISPs are the equivalent of the shops

The pictures emit photons which fly through the air to the child. The air is the shop.

Or for websites your computer is the shop.

The ISP is not the shop. Nor in the OSA is it viewed as such. The company who makes the service has some responsibility.

> So it would make a lot more sense to apply controls at the ISPs.

This fundamentally cannot work for what is in the OSA, and if you cannot see why almost immediately then you do not know what is in the OSA and cannot effectively argue against it. It is not a requirement to add age checks to porno sites.