I'm trying really hard not to nuke these tags out right, but people aren't making it easy. Danbooru is a porn site in the eyes of most outside observers, and a porn site with a tag for little girls immediately sets off red flags. It's hard to say this tag is for innocent images when so much of it is soft loli content. And it's hard to keep the tag clean when the whole idea of "I want to search specifically for pictures of little girls" inherently attracts people who don't have the purest of intentions.
Usually in anime there's some ambiguity surrounding the actual age of characters. "All characters are above the age of 18" and all that. But it removes all ambiguity when you explicitly say the character is a child. Then you better be sure the image is completely safe, otherwise it's a red flag. And frankly, so many people here are so coombrained by hentai that I don't trust them to recognize what is considered unsafe by normal people standards.
Danbooru is actually banned in multiple countries over content that is considered to be loli by their standards, but not by ours. A female child tag that is less than 100% safe is basically asking to be banned in more places. Just the word "child" on a porn site sets off red flags.
About a month ago, I switched from Amazon to a new email provider for sending Danbooru's emails. The new provider banned me after a few days because they considered Danbooru to be a porn site. Even though our emails don't contain anything remotely NSFW. I switched to another email provider, but it goes to show that when you're considered a porn site, you're constantly at risk of being banned by service providers who don't like what you do. To run a website, you need to deal with a lot of third party service providers, many of whom don't want to deal with porn sites. And of the ones that do, basically none of them are okay with loli, or anything remotely adjacent to it.
The way we (and other sites like Gelbooru and E-Hentai) deal with this is by trying to keep this stuff off the radar. But that's hard to do when we have tags like female child and male child explicitly labeling characters as underage, and being used as backdoor soft-loli and soft-shota tags.