A Researched Post in Two Parts:
Part 1.
Actually, the majority of the evidence show that pedophilic relationships (in and of themselves) are not nearly as harmful as is commonly believed.
Now, different circumstances, such as relation of the offender, nature of the relationship (whether it's a relationship, or a person repeatedly raping the victim,) and societal reaction if the deed is discovered CAN significantly effect the minors, psychologically and socially.
In regard to age of consent, the things needed seem to be
1. Understanding of the acts being discussed.
2. Understanding of the possible consequences that could stem from the discussed act.
and 3. Desire to follow through with the discussed act without force or even pressure, in a lucid state of mind.
That being said, I understood sex from around age 11, and from discussion this seems to be a fairly average age.
However, if the person is an adult or older peer, simply the admiration the minor may feel may be enough to provide internal pressure, should the older party ask for sex. A younger party may not want to let the older down...
This is, of course, conjecture.
At its face, if a minor understands sex and sees themselves on an even level as their partner, there is no reason (in the above definition of consent) why consent should be an impossible thing.
Now, about my above statements about pedophilic relationships not being as harmful, I base this on actual reports.
https://www.ipce.info/library_3/files/tomoc/sexpriv_backgr_text.htm
This report, among other things, investigates reports of sexual offenses against minors in countries during brief periods when this manner of pornography was legal, as well as the times just before and after.
It points towards an inverse relationship, the more porn on a subject, the less sex-crimes.
https://www.sciencedirect.com/science/journal/01602527/22/1
This article shows a similar relationship between pornography and sex crimes, in Japan.
More sources that support this are:
https://www.sciencedirect.com/science/article/pii/S1359178909000445
http://idei.fr/sites/default/files/medias/doc/conf/sic/papers_2007/kendall.pdf
Given that information, making possession (but not necessarily production) charges illegal may actually reduce the number of CSA incidents.
Let us, then, move on to content of this pornography.
In regard to this type of pornography, roughly 1/3 involves adult intercourse with minors, nearly half is erotic nudity or genital display, and the rest is sexual acts involving children.
https://www.bookdepository.com/Child-Pornography-Ian-ODonnell/9781843923565
These statistics are not terribly important now, but may be useful later.
(note, given a broader definition of pornography, these numbers are much different, including <1% involving adults.)
http://www.tandfonline.com/toc/wjhm20/56/2
Now for this pornography's effect on the children involved.
Above-mentioned articles by Ian O'Donnell and by H. Mirkin show less harm than previously though.
But I'll let some of the children speak for themselves.
http://www.ipt-forensics.com/journal/volume4/j4_2_1_5.htm
These boys were part of a pornographic ring, had positive feelings about their abuser, and negative feelings about the police who ended the operation. They chose to remain in contact with the abuser even as adults.
They claim that the worst aspect of the photography as children was the betrayal of trust when the photographer (who was not essentially their abuser) sold the photos internationally.
My next source is not as clear:
The starter of this thread claims to be a boy pedophiles know as "spongebob" in a quite well-noted case.
He expresses many ill feelings about himself, and his offender, but it should be noted that he hates his offender for the same reason that the boys above hated their photographer. A complete betrayal of trust by the pornographer.
It may be noted that reports show the boy exhibiting positive changes in behavior during the times when the relationship was active. I do not know if this is actually the boy, but he does not seem as biased as one would expect an undercover pedophile or "antipedo" would be.
https://www.reddit.com/r/casualiama/comments/2tj10p/i_was_the_kid_behind_the_spongebob_child_porn_case/
This is quite in line with other reports, such as the infamous Rind, et al. report which showed a significantly lower relationship between cases of CSA and self-reported harm.
http://digilib.bc.edu/reserves/sc563/mcgu/sc56310.pdf
It should also be noted that Kinsey's books on Human Sexuality also show sexuality and sexual knowledge as present well before the age of 18.
All of this, plus the information that much of the material produced today is made, in fact, by minors, paints a radically different picture.
http://www.independent.ie/irish-news/children-producing-their-own-web-porn-26454111.html