Another possibility could be Jarvis, or in the later versions, Friday. They are AI systems that are used to looking after Tony in a way. They could help with things like making sure the environment is safe for baby Tony, and providing information on how to take care of a baby, if needed.
Pepper would be a likely candidate. She has a close relationship with Tony already, so she'd probably step up and take care of him. She has experience dealing with Tony's antics, so she could handle baby Tony's needs too.
Catwoman might also step in. Despite being a sometimes - villain, she has a soft spot for Batman. She could use her cat - like skills to keep baby Batman out of harm's way. And she might find the whole situation rather amusing, but still be very vigilant in protecting him.
In this kind of fanfiction, there could be a lot of humorous situations. For example, the Avengers might be super confused at first. They'd have to take care of baby Tony like he's a little, fragile thing. Maybe Pepper would be like a mother figure, trying to figure out how to handle a baby genius. And Tony, as a baby, might still show some of his intelligence in really cute ways, like tinkering with small gadgets even at that young age.
I think Konan would be the most likely. She has a more gentle and nurturing side compared to most of the other Akatsuki members. She could use her paper abilities to create things for the baby like a soft bed or toys.
Mercy could also be a great caretaker. She has a nurturing side as a healer. She would be able to make sure baby Junkrat is healthy and well - taken care of, using her medical skills to check on him regularly.
France would be a likely candidate. France has always had a sort of motherly - like affection for Canada. He would probably be very eager to take care of baby Canada, dressing him up in cute clothes and feeding him French cuisine, like crepes.
Japan could also be one to take care of baby Italy. Japan is known for being meticulous and organized. He might be able to handle the practical aspects of taking care of a baby like preparing proper baby food and creating a clean and safe environment for baby Italy.
It could be Remus. He is the most level - headed of the group. He would be patient and understanding with a baby. His calm nature would be well - suited for taking care of baby Severus.
Iruka - sensei would be a likely candidate. He has always been like a father figure to Naruto, so he would probably step up and take care of baby Naruto.
In this fanfiction, Tony Stark's character would develop in several ways. Initially, he might be a bit clumsy at parenting, but as time goes on, he'd become more attuned to Peter's needs. His focus would shift from just his own inventions and heroics to also considering Peter's future. He'd become more selfless, as he'd be willing to sacrifice his time and resources for Peter's well - being. He might also become more cautious in his actions, knowing that he has a young life depending on him.
Some fanfictions might make it an unexpected character. For instance, a female superhero from another universe who somehow crosses paths with Tony Stark and they end up having a baby. This would open up all sorts of new story possibilities, like dealing with different cultures and powers.