Well, they could time travel to a time when there was a great magical epidemic in the wizarding world. Hermione, with her vast knowledge of magic, tries to find a cure, and baby Teddy, who has a natural charm, helps to cheer up the sick and the downhearted. Or they could travel to a time where a new form of magic was discovered. Hermione is eager to learn about it and Teddy, with his adaptable nature, is able to quickly adjust to this new magic environment and even contribute to its understanding in some small way.
A possible plot is that they time - travel to the time when the Marauders were at Hogwarts. Hermione gets to meet James, Sirius, Remus, and Peter in their youth. Teddy, being Remus' son, has an interesting connection with them. Maybe they accidentally change some events related to the Marauders which then has a ripple effect on the future. Or perhaps they travel to a time just after the Battle of Hogwarts. Hermione and Teddy go back to help with the rebuilding process, and Teddy discovers things about his father's past through the memories of the survivors.
One plot idea could be that Hermione and baby Teddy travel back to the time of the founders of Hogwarts. There, Hermione uses her knowledge to help the founders with some magical problems they are facing, while Teddy, being a metamorphmagus, unknowingly reveals some future magical abilities to the wizards of that time, causing a stir. Another idea is that they travel to a time during Voldemort's first rise to power. Hermione tries to find a way to stop him earlier, with Teddy's unique abilities helping them to blend in and gather information. For example, Teddy could change his appearance to look like a Death Eater's child to get close to their secrets.
One idea could be that Baby Teddy Lupin time - travels back to the Marauder era. He could meet his father, Remus Lupin, as a young boy. This would create some really heartwarming and bittersweet moments as Teddy gets to see his father's early life and perhaps even influence some events in a positive way.
A great plot might be that Teddy time travels to a time when Harry was a child living with the Dursleys. Teddy could try to secretly protect Harry from some of the bullying and neglect he endured. Or perhaps Harry and Teddy travel to a time long before Hogwarts was founded to learn about the origins of magic in the wizarding world, and they bring that knowledge back to their own time to help improve modern magic.
They could time - travel to a time in Hogwarts' history when a great mystery was unsolved. Harry and Teddy could work together to figure out what really happened. For example, they might explore the mystery of the Chamber of Secrets long before Harry's own encounter with it. Teddy's inquisitive nature and Harry's experience could lead them to some amazing discoveries.
A possible plot in the Harry Potter Teddy time travel fanfiction could be Teddy going back to the time of the founders of Hogwarts. He could be a sort of mediator between the four founders, especially if there were some disputes or misunderstandings that led to future problems in Hogwarts. Teddy could use his knowledge from the future to try and smooth things over. This would not only change the history of Hogwarts but also have a big impact on the future wizarding world he comes from.
A third idea might be that both Harry and Teddy accidentally travel to a time in the past where a great magical event took place, like the founding of Hogwarts. They have to figure out how to get back to their own time while also trying not to disrupt the events that are crucial to the wizarding world's history. They might even learn some long - lost spells or magical knowledge during their time there.
Maybe baby Naruto time travels to a time when the Uchiha clan was still thriving. He could interact with the young Sasuke's family and somehow change the course of events that led to the Uchiha massacre. This would create a whole new timeline with different challenges and relationships.
Perhaps Naruto time - travels and ends up in a world where he is a baby again but with all his current powers and knowledge. He has to figure out how to use his abilities at such a young age without revealing too much. This could lead to some really comical and heartwarming moments as he interacts with the people around his baby self.
One idea could be that Hermione travels back in time and accidentally gets involved with Lucius in his Hogwarts days. Maybe she has to work with him to prevent a dark magic event that would have far - reaching consequences in the future. This could lead to a strange alliance where they start to see each other in a different light.
One idea could be that Hermione and Bill travel back in time to the founding of Hogwarts. They could witness the four founders making their decisions about the school, and Hermione, with her vast knowledge, might accidentally influence some of their choices. For example, she could suggest a different way of sorting students that gets incorporated into the Sorting Hat's initial magic.
One idea could be that Hermione travels back in time and accidentally changes something that affects James's future. Maybe she saves someone important to James that was supposed to die, and then they have to deal with the altered timeline together.