Hmm, 5'000 sounds way too high. Are they sure it isn't just people who log into 4chan or something like that which and gets called a child porn site because it has some loli on it somewhere? I'm not saying it's right, it's just people may have rather a skewed expectations thinking photographs when it could be drawings in some cases.
There also seems to be some worrying leaps of logic from the OP's source that are cleared up when going back the the original source of the Huffington post. The 5'000 figure was found not all WITHIN the Pentagon (which is only one relatively small office) but UNDER it as the ENTIRE Department of Defence which is The US Navy, US Marines, Coast Guard, Air Force, Army, Missile defence, manufacturing contractors, affiliates, etc, etc. That is TENS of MILLIONS of people! And this isn't even all at once, this is going back to 2007 and I think even before that.
The 5'000 figure is of ALLEGATIONS, which is NOT the same as charges or even convictions. I mean this is pretty hard to determine in the public space who is actually guilty as most of the time we can't legally even look at even representations of the evidence even if we wanted to. I mean crime scene photos can go in the public domain to be discussed but not this.
See it isn't black and white, like if it is an amateur porno video of a young looking woman who though clearly has reached puberty... but is she over 18? If she's 17, legally it's no different than if she was 12 in terms of child porn laws. But morally the difference is huge, I mean the age of consent in my country is 16 (and in many states in the USA) so people need to stop and think before they get indignant with: "why didn't they charge all these 5'000 people who were accused >:C"