The ToU says that to use FANDOM you must agree not to "Post or transmit any content that is obscene, pornographic, abusive, offensive [or] profane"
The Community Guidelines (which are part of the ToU) say "For text, content that just mentions characters have sex is likely to be OK. But content that describes exactly how they have sex, is not. Content that describes violent or non-consensual sex is expressly prohibited.". I'd add to that sex with underage characters.
I know you have an age warning on the main page, but that doesn't negate the limits in place in the ToU and Guidelines.
If you aren't able to fix this, you will need to find another host.