Captain America is very likely to be featured. He has that paternal, moral - compass kind of vibe. He would be the one to gently tickle the 'daughter' as a way of showing his soft side. Thor could also be a popular choice. His big - hearted and sometimes child - like nature would make for some great tickle - related antics with the 'daughter' figure.
Well, a common theme is protection. The Avengers, being superheroes, would be protective of their 'daughter' in these fanfics. When they tickle her, it could be a form of showing their care in a gentle way. Also, growth and development can be a theme. As the story progresses, the 'daughter' might grow in confidence or develop new skills with the support of the Avengers, and the tickle moments could be part of those positive interactions.
Tony Stark could also be a key figure in some fanfics, even though he's no longer alive in the main MCU timeline. His intellect and previous experiences with multiversal - related events (like in Endgame) could be explored in the fanfic. Maybe the Avengers find a way to access his knowledge or even a version of him from another universe to help them out.
Ant - Man would be a likely candidate as his power already involves size - changing. In fanfiction, his ability could be enhanced or malfunction, leading to all kinds of interesting scenarios. For example, he could accidentally make all the other Avengers the same size as him, creating a whole new dynamic for the team.
Thor would be one of the active ones. He has a lot to share from his Asgardian experiences. Hulk, well, he might not type much but when he does, it would be in short, powerful statements. And Scarlet Witch could be in there too. She could use her powers to sense if there's any danger approaching the chatroom or the Avengers themselves while chatting with the others.
Captain America is a likely candidate. He has a strong moral compass and a sense of protectiveness. He would see it as his duty to take care of the baby. His old - fashioned values would make him a great caregiver, like making sure the baby has a proper upbringing even in the middle of all the chaos in the Avenger's world.
Black Widow. She has a lot in common with Batman in terms of skills. Both are highly trained in combat, stealth, and espionage. They would understand each other's need for secrecy and their ability to operate in the shadows.
Hulk. He has a tendency to lose control and his large size could easily knock over shelves or accidentally break items.
Thor would be a likely candidate. Since he is Loki's brother, he already has a connection with him. Thor might be the one to convince the other Avengers to give Loki a chance and be the first to reach out and try to befriend him in this new situation.
Captain America would be a likely candidate. He's all about justice and if he thought Spider - Man was doing something wrong, he'd go after him. Also, Iron Man. He's often quick to act and if he saw Spider - Man as a threat to his technology or the safety of the world, he'd be on the chase. Black Widow too, as she's used to tracking down targets and if she was given the order to bring in Spider - Man, she'd do it.
One great 'Avengers tickle Peter' fanfic could be 'The Ticklish Spiderling'. In this fic, the Avengers find out about Peter's extreme ticklishness during a training session. It's full of light - hearted moments as they playfully tickle him to cheer him up after a tough mission.