How do you report suspected kiddie sites?

Ok. I watch a lot of internet . I mean a lot. A ton of....you get the point. Every other pic or video I click on always sends me to other sites. Sometimes the site I'm sent to looks like it's full of small girls. The pics are usually blurry, so you can't really tell if these are actually underage girls or really small women. Either way, yuk. No offense to small women. Anyway, my question remains. How do you go about reporting suspected sites without getting involved in it in the first place? I don't want to report a site then have the FBI come knock my door down, take my computer and put me in jail. Yeah, I'm slightly paranoid when it comes to the government. At the same time, I'm sick of seeing these damn sites. Surely that stuff is illegal all over. I don't see how the sites can exist in the first place without the FBI cracking down on them in the first place.