The other villains in Gotham. The power dynamic changes when the Joker is a kid. They might see this as an opportunity to take over his territory or try to use the situation to their advantage. But they also might be worried that if the Joker turns back to normal, he'll come after them for taking advantage of his weakened state.
Well, he might lose all his evil cunning at first. Since he's a kid, he could start to see the world in a more innocent way. Maybe he'll make friends with people he used to terrorize, not realizing who they are. And he could be easily influenced by good-hearted characters, starting to develop a sense of right and wrong that's completely different from his adult, villainous self.
Obviously, Bakugo would be one of the most affected. His relationship with Izuku has always been complex, and Izuku becoming a girl would surely change the dynamic between them. He might have to re - evaluate his feelings of rivalry and superiority. All Might would also be affected. As Izuku's mentor, he would need to adjust his training methods and support system to fit Izuku's new situation as a girl.
His friends would be affected. They might be both in awe and a bit worried about the new - powered Gaara. His siblings, too. They would need to adjust to this new version of Gaara who has Shukaku back.
It could also be a new villain. Maybe someone who has been waiting for Sonic to be in a vulnerable state. This new villain could have a special power or weapon that is more effective against Sonic as a kid. For example, a device that can slow down Sonic even more or nullify his powers temporarily. They might target Sonic not just because of his weakened state, but also because they know that his friends will be distracted trying to help him get back to normal.
The entire village of Konoha could be highly affected. Naruto, with his second chance, could bring about positive changes in the village much faster. For the younger generation like Shikamaru, Naruto's new approach might inspire them in different ways. And for the older generation, they might be forced to re - evaluate their views on Naruto and the future of the village if he starts making radical changes early on.
Obviously, Death the Kid himself would be the main character. He's the one who's sick after all.
If Deadpool is turned into a kid in fanfiction, it would be a total shift in his character dynamic. His relationship with other characters would change drastically. For example, his friends might have to take on a more parental role. And his enemies might not take him as seriously at first, but he could still surprise them with his child - like cunning. Also, his origin story would be interesting to re - imagine from a kid's perspective, how he discovers his powers and all that.
Well, in such a fanfiction, Sonic might lose his usual speed and confidence at first. He'd probably be more naive and rely on his friends more. Maybe he'd have to learn basic things all over again, like how to properly control his powers in his new, smaller form.
I think it could be Clint. He has a family and the thought of his family being Snapped away would be devastating. He would be haunted by the idea that he wasn't there to protect them. He might feel a great sense of guilt and loss compared to the others.
Natasha could also be greatly affected. She is perceptive and if she reads Tony's thoughts, she might use that knowledge to manipulate situations within the team for the better or worse. Maybe she discovers Tony's concerns about a potential threat and uses her skills to help address it.