The Avengers would react in different ways based on their personalities. Vision, for instance, might be very curious about the biological aspects of a human baby. He'd study Peter's little movements and expressions. Wanda would use her powers to create little floating toys for the baby to play with. They all would just be so smitten with baby Peter Stark and would do everything they could to protect and care for him.
Tony would be beaming with pride, of course. Natasha would be really gentle and might even sing a lullaby to the baby in Russian. Thor would pick up the baby very carefully, like he was handling something extremely precious, and his booming laugh would probably make the baby either laugh or cry. Either way, it would be a very emotional and cute reaction from the Avengers.
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.
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.
The Avengers might react in different ways. Steve Rogers would probably be polite but firm in getting to know Peter's boyfriend. He'd want to ensure that he was a good influence on Peter. Thor, on the other hand, might be a bit more boisterous. He could either be really friendly and enthusiastic, or his loud and powerful presence might accidentally scare the boyfriend a bit.
Well, the plot could be really cute. Maybe the Avengers are all shocked when they first see baby Peter Stark. Tony, being the proud father, shows off his baby to the team. They might all take turns holding the baby and trying to make him laugh. And perhaps Peter, even as a baby, shows some signs of his future genius, like being fascinated by some of the Avengers' high - tech gadgets.
Some fanfics show the Avengers being protective of Peter Stark. If he's a young and inexperienced character, Thor might take on a big - brotherly role. He could offer to train Peter Stark in combat or share his knowledge of different worlds. Iron Man, if not related to Peter Stark in that particular fanfic, might be a bit jealous at first of his intelligence but then realize they can work together for the greater good.
Well, if the Avengers meet Peter's girlfriend, it depends on their own personalities and what they've heard about her. If they've heard good things from Peter, some like Spider - Man himself would be very excited to introduce her. The Avengers might be a bit cautious too, because they don't want any harm to come to Peter or their team because of her. For example, if she has a past that's a bit murky, they'll be on high alert. But if she's just a normal, nice girl, most of them would eventually warm up to her, except maybe those who are more cynical like Loki (if he was somehow part of the Avengers in this fanfiction), who would always be suspicious.
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.
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.
They might be shocked at some of the dangerous situations Peter has been in without their knowledge. They could feel guilty for not being there to protect him more. And they would likely be very proud of his selfless acts.
The Avengers would initially be in shock when they find out Peter is sick. Clint Barton would be the one to keep a calm head and start organizing things. Wanda Maximoff would try to use her powers to ease Peter's pain if possible. Vision would use his vast knowledge to try and find a solution. They would all be very concerned and do everything they can to make Peter better, from getting the best medical help to providing a safe and comfortable environment for him to recover.
Obviously, baby Peter would be one of the main characters. Among the rogue Avengers, it could be Captain America if he goes rogue in the story. Hawkeye might also be there as he has a family - like side and could be sympathetic to baby Peter. And Scarlet Witch could be involved too, with her powerful magic.