"Alleged" child sexual abuse when these were clearly legal minors prostituted in a third world country notorious for catering to pedo-tourists:

At the center of the controversy is a series of images made in 1989 by American photographer David Alan Harvey that document sex workers in Bangkok and were, until recently, tagged in Magnum’s archive as “teenage girl – 13 to 18 years.” The entire archive has since been taken offline. A spokesperson for Magnum told The Guardian that the agency has not yet determined the accuracy of the tags or who provided them.

According to Fstoppers.com, Magnum’s website yielded more than 100 results with the search terms “girl prostitute.”

Many condemned the use of the word “historical” as a way for Magnum to absolve itself of responsibility for the images in question, many of which flout UNICEF’s guidelines for ethically documenting children.

This is the UNICEF website referred to:

UNICEF Photography promotes the appropriate use of images of children in all media. The accurate and respectful visual representation of children everywhere is part of defending children’s rights, including their rights to expression, privacy and protection. Recognizing that children are frequently at risk of abuse, discrimination, stigma or other exploitation if their name or visual identity is known, UNICEF promotes international photography norms that protect children’s identities – in both the making and the use of images of children – as needed.

https://www.unicef.org/photography/photo_about.php

When I type in "guidelines" into the search bar I get a bunch of hits but none pertaining specifically to photography. I did find this one paragraph about photography:

Taking photographs or videos: When using creative methodologies to involve children in research, particular care needs to be taken with photography or videos (Mann andTolfree, 2003), especially in politically and socially volatile settings, such as humanitarian settings. Prior consultations should always be undertaken with those best able to assess the political, social and cultural ramifications of taking or disseminating photographs in these contexts. Clear discussions are needed with children regarding permission from those portrayed in photographs or videos, and the potential dangers of these portrayals (UNICEF, 2015).

https://www.unicef-irc.org/publications/pdf/IWP_2016_18.pdf