Maybe a spell goes wrong and creates a baby that has a combination of their magical traits. They then need to figure out how to reverse the spell while also dealing with the sudden 'parenthood'. They might discover new sides of themselves as they care for this unique baby.
One idea could be that Harry and Draco find an abandoned magical baby and they have to work together to take care of it. This forces them to put aside their differences and learn about each other in a new way.
One idea could be the baby having a special magical ability that Draco and Astoria have to figure out how to handle. For example, the baby might be able to communicate with magical creatures from a very young age. Another plot could revolve around the baby being in some sort of danger, like a dark wizard targeting the family because of Draco's past. Or perhaps the baby's first year at Hogwarts, with Draco and Astoria being overly protective and the comical situations that arise from that.
One idea could be that Draco and Hermione's baby has unique magical abilities that draw the attention of both the wizarding world's good and bad elements. The baby might be able to communicate with magical creatures in an extraordinary way, leading to adventures where they have to protect the baby from those who want to use its power for evil.
A possible plot is that their baby is born with a prophecy attached to it. The wizarding law dictates that any baby with a prophecy must be placed under special protection and observation. Draco and Hermione, being protective parents, try to find a way to ensure their baby's normal upbringing while still adhering to the law's requirements. This could lead to a lot of drama and character development as they face opposition from those who strictly enforce the law.
Another plot could be that the baby project is a ruse by the teachers to get Draco and Hermione to reconcile the differences between Slytherin and Gryffindor. As they take on the project, they start to understand each other's houses better. The 'baby' becomes a symbol of unity for them, and they eventually fall in love while trying to raise it in the best way possible.
One idea could be that Harry and Draco find a magical toy that has the power to transport them to different wizarding worlds. They have to work together to find their way back home. Another could be that they both inherit a collection of enchanted toys from an old wizard, and they must figure out how to use the toys to solve a mystery in Hogwarts.
One idea could be a story where Harry, Draco, and Severus are forced to work together on a dangerous mission to save Hogwarts from a new dark threat. They start off distrusting each other but gradually learn to respect and rely on one another.
One idea could be a story where Draco, Harry and Hermione are forced to work together on a special magical project for the Ministry. They start off hating each other but gradually come to respect one another's skills. Another plot could involve them getting trapped in an alternate magical dimension where they have to rely on each other to find their way back. Maybe Draco has some knowledge of the dark magic that created the dimension, Harry has his Gryffindor courage to lead them through dangerous areas, and Hermione uses her vast knowledge to figure out how to break the spell that trapped them.
One idea could be that as a baby, Harry has some adult - like wisdom and he starts to subtly influence the adults around him in Hogwarts. For example, he might give Dumbledore some deep insights about the future of the wizarding world that Dumbledore hadn't considered before.
One idea could be that Harry and Daphne's baby has some unique magical abilities that are a combination of their genetics. For example, the baby might be able to communicate with magical creatures in a way that neither Harry nor Daphne can. Another plot could be centered around the challenges they face as new parents in the wizarding world, like dealing with over - protective relatives or the paparazzi - like wizarding press.
One idea could be a story that focuses on Draco's early childhood and how Lucius and Narcissa are trying to shape him into a proper pure - blood heir. For example, they might start teaching him about the importance of family heritage and magic lineage from a very young age.