I don't understand why people make this kind of story with heavy subject and especially when it involves children. I can understand if it's about child abuse and when it's only use to make feel more empathy with the character going through that. But here it feels like the author is going going to only give use torture porn with children... They have to stop doing that
First and foremost, it's fictional. No real life person of any age was harmed, so the author can do anything and everything. Child abuse as backstory to invoke empathy is ok, but it's not the only possible usage, the author is crafting a story, if they finds a new way to use an element that fits the story, then it goes into the story, that's normal. Moreover there are technical aspects to it: Heavy subjects would be even more heavy when they are inflicted on the weak and naive/innocent characters like children, and there are plot lines that only work if the characters are children...
I believe the readership/audience has the freedom to choose whether to consume a work, while the authors have the total freedom to create whatever story they could think of and could express into a presentable form. If one reader finds a story to be distasteful, then they should drop it and read other stories. It's not like the existence of a weird story would delete the existence or limit the growth of other "good" stories, it's no longer the age where books must be copied by handwritting and only a limited number of people knows how to write. The abundance of and the ease of access to information and works (fiction or otherwise) nowadays are unprecedented in human history, the choices are practically limitless. It makes no sense trying to impose what sort of story an author should or should not create.
It's not because it's fictional that you can say and draw everything you want. It's not because they were not real persons harmed that you can show the more hateful and immoral things in your story. Words and pictures have meanings and can be more harmful and impactful than any physical actions. This stupid argument and the other "people choose what to read" are the things that lead us to have story (manga, anime, BD, comics ....) that show and spread harmful ideas that actually hurt real people.
And in this case, there is nothing to justify the choice of actor to show little children being abuses and one of them impregnate by her dad ? WTF !