Tiger, Tiger by Margaux Fragoso
Nonfiction but written like a novel. Memoir by a woman who had a 14 year long relationship with a pedophile, aged 8 to 22. Fragoso isn't afraid of portraying the ambiguities of the relationship, saying that she loved him and that he was her soul mate, but also describes the psychological abuse that went both ways.

Lamb by Bonnie Nadzam
A novel about a man who takes an 11 year old girl out of the scummy suburbs of Chicago and on a road trip across the Rockies to show her beauty. They do have sex but this isn't the focus of the story however. Amazing prose. Has a decent film adaptation too.

The She-Devils by Peter Lewys/Pierre Louÿs
Translation of the French Trois Filles de leur mère. Hardcore erotica about a man who has sex with a woman and her three daughters, the youngest of them being 10, all of which are prostitutes. Lots of anal. I mean it, there is a lot of anal in this book.

The End of Alice by A.M. Homes
Very well-written novel about an incarcerated male girl-lover who receives letters from a female boy-lover who is at large and grooming a child. Deeply disturbing. I actually couldn't finish it because one part hit too close to home. I might give it another shot though.

Erotic Innocence by James R. Kincaid
Nonfiction. Book by an English professor that examines the (largely mythological) narratives society constructs about pedophilia and concludes that they are the legacy of Victorian sexual morality.

Mine-Haha, or On the Bodily Education of Young Girls by Frank Wedekind
I haven't actually read this one yet, and I'm not sure how pedo-related it really is. It's a surrealist novel about girls going through puberty. I did however, see the 2005 film adaptation recently which had a lot of naked children in it. Also a very good film 10/10.

BONUS ROUND: ART BOOKS!
The Age of Innocence by David Hamilton (or any of his books really)
Erotic photography art book whose subject matter is entirely focused on young girls, who are often semi-nude, accompanied by prose and poetry quotes. Out of print collector's item, very expensive but a .pdf is easily found online.

Futurelog by Murata Range
A collection of the legendary loli artist's work spanning several years.

Show Me!: A Picture Book of Sex for Children and Parents
Photographic sex education book for children. Highly praised in Europe, but actually banned as CP in the United States of Puritan Zionist Faggotry. Features many photographs of happy children in the nude and having sex. Also an out of print collector's item, but a .pdf is easily available online if you search by its German title.