Hinata herself, in a way, would be affected. Even though she's a baby, she might still have some sense of her old self. And she'd be in a situation where she has to rely on others completely, which is very different from her normal self - reliant nature.
The Hyuga clan would also be deeply affected. Hinata is an important member of the clan. Her turning into a baby would disrupt the clan's plans and they'd be worried about her future and her role within the clan. They'd likely be scrambling to find a solution.
I think Naruto would be one of the most affected. Since he and Hinata have a special connection, having her turn into a baby would completely change their dynamic. He'd have to step up and be responsible in a new way.
Lucy would be very affected. She's one of Natsu's closest friends. She'd have to take on a lot of responsibility for taking care of baby Natsu, which would disrupt her normal life of doing quests and writing her novel.
I think Sango would also be greatly affected. As a female in the group, she might feel a stronger sense of responsibility towards baby Kagome. She would be worried about how to take care of her properly, especially in their rather dangerous world full of demons. And she might also be concerned about how this would impact their overall mission and group dynamic.
In this fanfiction, it could be that Hinata's memories are still somewhat intact even as a baby. So she might still show signs of her shyness towards Naruto. She could blush when Naruto gets close to her while taking care of her. And perhaps, this situation could lead to Naruto realizing his deeper feelings for Hinata in a more protective and caring way. He would start to see her in a different light and understand how important she is to him on a whole new level.
His powers would likely be severely limited. The Sharingan, which requires a certain level of mental focus and chakra control, would probably not work as effectively. As a baby, Sasuke's chakra system is not fully developed, so he might not be able to access the full potential of his powers. He might only be able to use the Sharingan in short bursts, like when he's really scared or in immediate danger.
It's possible that his powers would be more erratic. As a baby, he doesn't have the control he has as an adult. So, his ice - making abilities might go off randomly. For example, he could accidentally freeze the water in a nearby pond just by being near it while having a little tantrum. But as he grows and learns about his powers again, he would start to gain more control over them.
Hinata's family would also have to deal with the emotional aspect. They love Hinata in her normal state, and now they have to adjust to this new form. They might start to remember when Hinata was actually a baby before and all the hopes and dreams they had for her then. Some of the more conservative members of the family might be more hesitant to let Naruto be around her, but the more open - minded ones could see that Naruto's presence is actually good for her in this state. And they would all be united in their goal to get Hinata back to her normal self.
His powers might be affected in different ways. For example, his web - shooting ability could be less precise. Since he's a baby, he doesn't have the same muscle control and coordination as his adult self. So, the webs might come out in a more random direction.
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.
Well, one possibility is that Naruto would be extremely protective. He has always cared for Hinata in some way, and with her as a baby, he'd likely take on a very nurturing role. Maybe he'd try to find a way to turn her back, or he'd just enjoy taking care of her like she was his own little sister or something. He could introduce her to all his friends in the village as his 'new little friend' and they'd all be super curious about how this happened.