Okay, all R18 genres are unhealthy to read, especially for children (underage). The R18 label is no joke. Make sure you supervise your children. Don't let children's innocence be ruined by unhealthy stories.
And as for healthy genres? I can say that all stories designed from the start to teach moral values/human values are very healthy to read, even if they are heavy genres such as psychological, tragedy, horror, and dark fantasy. Because these stories teach us to appreciate, love, accept flaws, have empathy, and learn to be "human."
By reading psychological, tragic, and even dark stories, we learn to feel the suffering of others without having to experience it directly. This fosters empathy and compassion. This allows us to better understand others' feelings, thoughts, and even weaknesses without judging them.
"Humans will never be able to understand each other if they do not share the same suffering." - Pain (Naruto)