Porn sites should do what NeoGAF did (no, not THAT thing they did). You'll need to register with a 100% authentic, formal email address. I think that's like an email that would come with your ISP provider. Or an email you'd have to pay for.

If anything, you should definitely register an account to view them. And you should be required to answer questions that a small child is very unlikely to answer correctly. Protect the children.