Your thoughts and fantasies are your own.
Nobody can even call you disgusting for having them.
The act is the crime. And that act starts before you actually rape a child.
Possessing child pornography is also the act, because even if you are not doing it yourself, you are taking pleasure in something in which somebody was hurt to produce.
I also want to bring up the issue of age of consent. This is dangerous territory, but I want to bring it up.
Ephebophilia is the attraction to adolescents. Not children. Some would argue that this is not a bad thing as teenage girls are able to reproduce, and therefore is not unnatural biologically. It is, however, culturally.
I've researched the subject. Most countries that I could find, the legal age of consent is 14. This includes our neighbor in the great white north, if I'm not mistaken. (Am I? Anyone from Canada here?) In Spain, it's 13. 16 is also very common. In fact, many states in the US seem to have the age at 16. So the whole idea of "it's disgusting if she's under 18," is stupid. 18 is not a magic number, and Britney and the Olsen Twins did not suddenly become hotter or "available" on their birthdays. I've met 18 year olds who act like they're 14. I've met 14 year olds who act like they're 18.
So the issue comes down to culture. I have to agree with the number 18, and I think that not only should every state set it at 18, but set marriage at 18 as well. Some states actually have the marriage age lower than the sexual age.

18 is a good number for our culture. But that being said, I still don't think it's wrong to have desire for someone under 18.
Yes, I'm 26, and yes, I've had these thoughts myself. Many times. And I know I will again. But I also have a fetish for older women. I'd much rather be stuck on a desert island with a MILF who knows what she wants and hates playing games than a 15 year old drama queen any day of the week. And I don't want to see "eewwww too much information" either. This is a serious discussion.
So am I evil and disgusting? No. I will never dream of manipulating a young girl into sex. Or jerking it while watching her through the window. I've never done either of those things, and if I ever do, I will turn myself in and willfully subject myself to shock therapy. Ask for it even.
Why? Because the question of culture. She is biologically ready, but in our society it would take manipulation to achieve, and therefore is wrong. As for Spain with it's 13, I think that's a bit low, but then again, I don't know how people think there either. Then again, there are places in the Middle East, I think, where it's 9, and there's no way in hell around that.