Laws against the depiction of fictional characters in sexual situations contain a tragic irony: because there are no actual victims, there is no way to prove one’s innocence (which is what one effectively has to do when charged with child pornography or some similar crime). You can’t have someone go to the alleged victim and confirm whether they are of legal age or not. It’s all subjective, making it impossible for an artist to be sure if it’s lawful or not.
You can make sure you’re not breaking the speed limit by checking your speedometer. You can make sure you’re not selling sexually explicit material to minors by checking IDs. You can avoid violating age of consent laws the same way. How do you verify the age of a fictional character?
This limits the kinds of stories you can tell, and how you can tell them, and it does so with no apparent benefit to any real person. Except perhaps people who want to limit the kinds of stories you can tell…. It’s not “for the children”, because there are no real children involved. It’s just a tool for the government (or people using the government) to control what other people can say, and what ideas they can express.
It’s a violation of free speech, and protects no one. At least no one real.