Well, in this kind of fanfiction, Naruto raising his past self could have a huge impact on the overall Naruto universe. He could change the course of many events. For example, he might be able to prevent some of the Akatsuki's earlier schemes by having his past self be more aware. His past self could also grow to be an even stronger ninja faster, as he has the guidance of his future self. This could potentially change the power dynamics in the Hidden Leaf Village and how they deal with external threats.
At first, it might be a bit strange. His past self would be confused and a bit scared of this older version of himself. But as time goes on, they would start to trust each other. Naruto would be patient with his past self, and his past self would start to look up to him.
One aspect could be Naruto training his younger self to be a better shinobi. He'd share his battle experiences, like the fights against Haku and Zabuza. His younger self would learn from his future self's strategies and become a more formidable ninja at a younger age. Also, Naruto could help his younger self understand the power of the Nine - Tails in a more positive way, instead of just seeing it as a curse. This could lead to his younger self being more confident and in control of his abilities much sooner.
In this fanfiction, Naruto would likely face many challenges. He'd have to provide for them, protect them from the village's possible discrimination, and also teach them ninjutsu. He might struggle to balance his own ninja duties with his new role as a caregiver.
Well, if Danzo raises Naruto, Naruto's relationships would be drastically different. He might not have the same bond with Iruka or his friends from the Academy. Instead, he'd be surrounded by Danzo's followers. His attitude towards the Hidden Leaf might also change. He could be more obedient to the village's darker side, which Danzo represents. But at the same time, Naruto's own spirit of hope might conflict with Danzo's methods, leading to internal and external conflicts in the fanfiction.
He would become more responsible. Naruto has always been a bit of a wild card, but with siblings to look after, he'd have to think twice before acting impulsively.
Well, it could start with Natsu accidentally stumbling upon a time - related magic or a magical artifact that transports him to the time when his past self exists. Then they would meet and there would be a moment of shock and confusion.
Well, Naruto would surely pass on his adventurous spirit to Hanabi. She'd probably be more willing to take risks and explore new areas of the ninja world. Naruto might also train Hanabi to be a better fighter. He could use his experience from his own training with Jiraiya and Kakashi to design a special training regime for her.
One possibility is that Naruto would finally experience the love and guidance of his parents that he always longed for. Minato could train him from a young age, passing on his powerful jutsu. Kushina would be there to comfort him when he's sad. They could all have family dinners together, and Naruto would grow up in a warm and loving environment, which would likely make him a more confident and less lonely child.
If Naruto is sealed in his younger self in a fanfic, it could be chaotic. His chakra control might go haywire as his younger body tries to adapt to the sealed future self. The village elders might notice something strange and try to investigate. His training with Iruka Sensei could take a whole new turn as he might show advanced skills too early. This could also have an impact on the Nine - Tails within him. The Nine - Tails might react differently to this new situation, perhaps becoming more or less aggressive depending on how the seal affects Naruto's mental state.
In this fanfic, Naruto might teach his younger self some advanced jutsu. For example, he could show the younger Naruto how to better control the chakra for Rasengan at an earlier stage. This would make the younger Naruto stronger faster in the story.