There might also be appearances by Harry Potter and his friends. Since it's a fanfiction related to the Harry Potter universe, they could play important roles, either as mentors to the Rose Child or as characters who are initially suspicious of the Rose Child but then come to understand them. Hermione, with her vast knowledge of magic, could be helping the Rose Child understand their powers better. Ron could be the one who provides some comic relief during tense situations involving the Rose Child.
There could also be new characters created specifically for this fanfiction. Maybe there's a mysterious wizard or witch who has some prior knowledge about the Rose Child and is either guiding or trying to manipulate them. Or perhaps a group of young wizards and witches who become friends with the Rose Child and go on adventures together in the wizarding world.
Harry Potter would definitely be one of the main characters, since it's about him being the 'child of death'. There might also be his friends like Hermione and Ron, as they are often involved in his adventures.
It's possible that the main character is the 'dark child' of course. There could also be a mentor - like figure, maybe an older wizard who tries to guide the child towards the light. And it wouldn't be surprising if there were some antagonists as well, such as other dark wizards who want to use the child's power for their own evil purposes.
It's difficult to determine exactly, but if the fanfiction focuses on the concept of the 'child of the green' being a new addition to the wizarding world, then that character would be central. There could also be other important characters like Draco Malfoy. Since Draco is from Slytherin, his path might cross with the 'child of the green' in interesting ways. And of course, we can't rule out the possibility of some magical creatures being significant characters in this fanfiction as well, like a magical snake or a forest - dwelling creature, considering the 'green' theme.
Obviously, the child is one of the main characters. There might also be some prison guards who play important roles, either as antagonists or those who gradually change their views towards the child. And perhaps some other inmates who interact with the child could also be considered main characters.
I'm sorry, without reading the fanfiction it's hard to say for sure. But it could be an original character created for this story, along with some well - known Harry Potter characters like Harry, Hermione, or Ron who interact with this new character.
Since it's about Harry Potter being death's child, he is the central figure. However, Dumbledore could also be a significant character as he was always guiding Harry in the original series and might have some knowledge about this new aspect of Harry. Additionally, Voldemort could be an important character too, as his relationship with Harry was always about life and death, and this new concept in the fanfiction could change their dynamic.
Hermione could be a main character. She's smart and resourceful. If there's a child involved and a case of mistaken identity regarding the child's parentage, Hermione would surely be involved in sorting out the truth, using her knowledge of magic and logic.
Hermione Granger might also be a central character. Her thirst for knowledge could lead her into situations where she is in the dark, like exploring a new area of magic that has many unknowns. As a child in Hogwarts, she might be trying to solve a mystery that no one else has been able to, and she has to start from a place of not knowing much, or being 'in the dark' so to speak.
Often, Harry Potter himself might be involved. Since he was an orphan, he could be a key figure in understanding how child services work or how they could have been improved in his case. Hermione could also be involved as she is very much into social justice and would likely be interested in the well - being of children in the wizarding world. And there could be original characters created by the fanfiction author, like a dedicated child services worker who is trying to make a difference in the lives of magical children.
Obviously, Harry Potter himself often makes an appearance. He could be a mentor or just a character that the new child of magic looks up to.