Unfortunately porn is a massively grey area, and has no universal definition. For example, I can go to www.thesun.co.uk and within one or two clicks be looking at topless ladies. Should the Sun be made to move over to .xxx?
What about Loaded magazine - very similar story, only the pictures are slightly more suggestive, but not actually any more explicit.
So what is porn? An American judge described pornography as "any act that has no artistic merit, and causes sexual thoughts".
Ever seen a TV advertisement? At least half of them could be defined by this statement.
The only difference I can see is that porn is open about the fact that it's supposed to be sexually stimulating. Advertising isn't, which in my opinion actually makes it more dangerous.
Of course, I don't think it's a good idea that children should be exposed to explicit material at an early age, but I also don't think they should be exposed to violence or gratuitous marketing.
In the immortal words of Bill Hicks, "Since when did sex become a bad thing?". Society needs to change its attitudes towards sex (and violence, and
definitely advertising) and maybe when we're all a bit less hung up, we either won't want to see porn any more (or as much), or we will at least be grown up enough to discuss it with our children should they happen to see it.
You don't need to go to a newsagent to see porn outside of the internet. When I was in primary school I can think of 2 seperate occasions when I found porn mags on the way to school. They scared me a little

Whether you agree with it or not, porn is out there, it relates to a natural impulse within us, and is unlikely to go away. Legislating against it is likely to make it more of a problem IMO. People like sex - let's get over it...