Great question! I certainly am not an expert, but I (from my super sensitive point of view) will throw my two cents in.
I certainly agree with what was said here about not shying away from the topic. I believe as Christians, we are uniquely positioned to talk about abuse and evil because we see the hope and goodness that can come out of it. I think we more than anyone should be addressing these issues in a loving and respectful manner.
That being said, I agree with @ncstokes that you need to be careful to guard your heart as you write about it. I know there are evils in the world and on the news that I have to stop looking for because it’s too dark and painful for me, and takes me into dark places and away from what God says to fill our minds with (Philippians 4:8).
A few thoughts on it (suggestions, not rules. I won’t be offended if you disregard any of them. Remember, I’m a more sensitive reader).
Make sure you frequently come back to brighter things. I wouldn’t leave your story dark all the way through, but pepper it with truly happy, and even funny, moments. It also adds to the depth of the sad parts (a great example of this is The Bookthief. That story made me laugh at parts and sob at others, and helped me appreciate the horrors by reminding me of the good things).
I would also try to focus on the effects of the abuse more than the actual acts themselves. That would allow you to explore the darkness without ever being too graphic. Though that’s from sensitive me, so it may be wise to disregard the suggestion.
I hope this helped in any way. I’m so glad you’re trying to tackle these hard issues in ways that are God-glorifying.
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...Just like everyone else