In fanfiction, their first child might face some challenges. Since Harry is so well - known, the child could feel a lot of pressure to live up to his father's reputation. The story could revolve around how the child overcomes this pressure, perhaps with the help of Ginny's wise advice and the support of their friends. The child could also have a special bond with Ron and Hermione's children, and they could all get into mischief together at Hogwarts.
Well, in fanfiction, their second child could inherit some unique magical abilities. Maybe it could be a super powerful healer, like having an extraordinary gift for curing dark magic -inflicted wounds that even advanced potions can't fully handle. This would make the child a target for some dark forces who want to either use or destroy this power.
Neville could also be a godparent. He has proven himself to be a brave and reliable wizard. After all his growth throughout the series, he could be a great influence on Harry and Ginny's first child, teaching them about the importance of perseverance and believing in oneself.
One possible storyline could be that the third child discovers they have a unique magical ability that neither Harry nor Ginny have. For example, they might be able to communicate with magical creatures in a way no one else can. This could lead to all sorts of adventures as they explore this new power and how it can be used for good in the wizarding world.
One possible reason could be miscommunication. Maybe they had a big fight over how to raise their child and Ginny, feeling unheard, decided to leave. Another reason might be external pressure. For example, if some dark forces were targeting their family again and Ginny thought leaving would keep Harry and the child safer. Or perhaps Ginny had some personal issues she couldn't deal with while being in the family, like feeling she lost her own identity in the relationship.
One possible plot could be that the child from the future comes back to prevent a great disaster. Maybe a dark wizard in their future time has found a way to rewrite history and the child has to make sure Harry and Ginny meet and fall in love at the right time. The child might also have some special powers inherited from their parents which they use to face various challenges in the past.
One plot twist could be that Harry is actually protecting Ginny and the real father. He might know some dark secret about the father that would put them in danger if it were known, so he pretends to be in the dark about the situation.
The remnants of Voldemort's followers could still be a threat. They might see the third child as a symbol of the new hope in the wizarding world that they want to destroy. Maybe they believe that the child has some sort of power that could ultimately be used to completely wipe out their dark ideology, so they target the child.
In some fanfictions, their first kiss might happen after a Quidditch victory. Ginny, flushed with excitement from winning the game, and Harry, proud of her, get caught up in the moment. Their eyes meet, and without thinking, they share a quick, passionate kiss as the rest of the team cheers in the background.
One possible plot twist could be that Ginny has some ulterior motive for lying. Maybe she wants to protect Harry from a greater danger. For example, there could be a dark wizard threatening to harm Harry's family if Ginny doesn't create this false narrative. Another aspect could be the reaction of the wizarding community. Some might believe her immediately, while others might be skeptical. This could lead to a divide in the community, with some supporting Ginny and some trying to expose the lie. Also, how Harry reacts when he discovers the lie would be a major part of the story. He might feel betrayed at first, but then as he uncovers the reasons behind it, he could come to understand and forgive Ginny.
It could be someone completely new, an original character created for the fanfiction. Maybe a mysterious wizard who had a brief encounter with Ginny.