Superhero and any other genre could attract kids, the stuff is allowed in comics because those comics are meant for a specific audience, now, is not the author's responsability if the parents go around leaving stuff in their children's hands without checking the Rating or just leaving their children unsupervised.
I'll be honest to you pal, many kids go into adult spaces just because they are curious regardless if there are adults telling them no, and a warning a sign, or even paywalls do the contrary effect, kids are way more interested in breaking those rules and barriers just to get their hands into that stuff, because they want to.
And I speak as someone that knew what hentai was at age 12, got her hands in doujinshi, video-games, movies that weren't suitable for my age, why? Unsupervised and also I was stubborn enough to make fake accounts and fake my age.

Like, with any game, movie, tv series, book, etc. There is a warning or label for stuff.






Thus, you'll be able to see those labels in content, its up to you to do your own research before handing something to a kid, or leaving them unsupervised. The issue is not the content itself, but how much of an absent parent you could be while being under the same roof. Or well, there are parents that simply don't care. One thing is normal, its easier to blame a creator than to blame the person that is actually responsible and legally the guardian of said kid.
To put an example, Deadpool is classified as a PG-13 movie in Argentina, while in other places is for +15. And still I've seen kids under 6 going to see the movie accompanied by their parents.