Maybe in the fanfiction, the Avengers initially think Peter Stark is just a regular kid related to Tony Stark, but then they find out he has the ability to time - travel. This would completely shift the story as they would have to deal with the implications of time manipulation and how it affects their missions and relationships.
A great plot twist could be that Peter Stark is actually from an alternate universe. He might have different values or powers compared to what the Avengers expect. This discovery could lead to a lot of conflict as well as new alliances within the group. They would need to figure out how to handle this unexpected visitor from another dimension.
Since he might be related to Tony Stark, there could be an emotional connection for the other Avengers. They might feel a sense of obligation to protect him or guide him, which changes their group dynamic. For example, Captain America might take on a more father - figure role towards Peter. Also, his presence could create some jealousy or competition among the Avengers who want to be his mentor or closest ally.
They would be all over him! Steve would probably have a big, warm smile on his face and just be in awe of how small and precious he is. Clint would make silly faces to make the baby laugh. Bruce might be a bit more cautious at first, but then he'd be charmed by Peter's little giggles.
One possibility is that the Avengers are facing a threat related to some old Hydra experiments that Howard Stark was once involved in. They meet him to gather information about the experiments, like the location of hidden files or the identities of key Hydra operatives from that time. Howard Stark, being the brilliant mind he is, joins forces with the Avengers to stop Hydra's resurgence.
There's a fanfic named 'Peter Stark and the Avengers: A New Alliance'. In it, Peter Stark might bring a fresh perspective to the Avengers. He could be the one to solve a complex problem that the Avengers have been struggling with using his unique intellect. Maybe he comes up with a new strategy to defeat a powerful enemy that the Avengers hadn't considered before. Fanfics like these often explore the relationships between the established Avengers characters and this new, interesting addition of Peter Stark.
One possible plot twist could be that the real danger was not what it seemed at first. For example, while the Avengers thought they were being attacked by a supervillain, it was actually a test set up by a greater power. And Peter discovers this truth while trying to save them. Another twist could be that Peter has to sacrifice one of his powers temporarily to save the Avengers, which changes his approach to being a superhero.
Perhaps in the fanfiction, the Avengers meet future Morgan Stark who has been trying to carry on her father's legacy. She might be leading a new group of heroes, and the Avengers could team up with them to face a common enemy. For example, she could have developed advanced Iron Man - like suits for her team. The story could also explore how the Avengers react to seeing the grown - up daughter of Tony Stark and how she has been influenced by her father's sacrifice.
The plot could twist when it turns out that the real danger the Avengers are in was set up by someone close to Peter. It could be a friend or a teacher who has been secretly working for a super - villain. Peter has to overcome the shock of this discovery and still find a way to save the Avengers.
A common plot twist is that Kid Tony turns out to be a key to solving a major problem the Avengers are facing. For example, in one fanfic, a powerful enemy has a shield that can't be broken, but Kid Tony figures out a way to disable it with his unique understanding of energy fields.
One possible plot twist could be that Peter's identity as Spider - Man is revealed to the public much earlier than in the original story. Since Tony Stark is his adopted father, he has to use all his resources and influence to protect Peter from the various threats that come with this exposure. This could lead to a lot of interesting scenarios, like Stark having to face off against some of his own business rivals who might want to use Peter's powers for their own gain.
In this fanfiction, perhaps the rogue Avengers are hiding out when they hear baby Peter crying. They initially think it's a trap but then realize it's just an innocent baby. Some of the Avengers might want to take him with them because they see his potential, while others are more hesitant due to their own precarious situation.