Iruka Sensei is a must - include. He was one of the first people to truly believe in Naruto when he was a kid. In a fanfiction with Boruto, Iruka could be the one to bridge the gap between the two generations. He could share stories of Naruto's past with Boruto, and also be there to support both of them in their ninja adventures. And of course, the new generation characters like Sarada can also be included. She and Boruto have their own dynamic, and adding her to a story with kid Naruto can create interesting interactions and storylines.
Definitely Sasuke. His relationship with Naruto is so important in the original story, and when it comes to a fanfiction with kid Naruto and Boruto, Sasuke can act as a mentor or a challenging rival for both of them. Another great character is Hinata. She has a special connection to Naruto, and in a fanfiction, she could play a role in guiding Boruto or providing support to kid Naruto in a new situation.
Shikamaru is a smart choice. His intelligence can be used to solve problems that Kakashi, Naruto and the others face. And his lazy - but - actually - really - smart attitude can provide some comic relief. Also, including the Third Hokage can give the story more depth, as he is the leader of the village and has a lot of knowledge and influence over the kids' lives.
Well, obviously Naruto and Hinata should be included. Naruto as the father can give some wise advice to Boruto and Himawari. Hinata as the mother can show her love and care for them. Also, Shikadai could be a great addition. He is Boruto's friend and his calm and intelligent nature can contrast with Boruto's more impulsive side, and he can also interact with Himawari in an interesting way.
Obviously Naruto and Boruto themselves are very popular. But characters like Hinata, Naruto's wife, also add a lot to the family dynamic in fanfiction. Sasuke is another one, as he has a complex relationship with Naruto and can be involved in the story in many ways. For example, he could be a mentor to Boruto. And of course, the older generation like Kakashi can also be included to give some wisdom and guidance to the family.
Sherlock Holmes is a great choice. His deductive skills would contrast well with Kaito Kid's thieving skills. Another good one is Lupin III. They are both master thieves, and a crossover between them could be full of interesting heist scenarios. Conan Edogawa would also be interesting. Since he's always trying to catch Kaito Kid in the original series, a crossover could explore new dynamics between them.
Hermione is always a great character to include. As a kid, she could be shown solving even more complex problems than in the books. Her intelligence and determination can drive the plot forward in fanfiction.
Sally Jackson, Percy's mother, is also an important character. Her love for Percy and her strength can be a central part of the story. She could be the one who gives Percy the emotional support he needs when he's confused or scared about the strange things happening around him. In a fanfiction, she could also have some secrets of her own related to the mythological world that Percy discovers as he grows up.
Well, obviously Naruto and Hinata should be included. Naruto could offer some words of wisdom to Boruto and Himawari as they face different challenges. Hinata can be the nurturing mother figure who is always there for them. Another great character to include could be Sasuke. He could train Boruto and Himawari in some new ninja techniques.
Sarada is a very popular character to include. She has her own goals of becoming Hokage and her Sharingan gives her a lot of potential for interesting storylines. For example, she could be on a mission to unlock new powers of her Sharingan.
Obviously Naruto and Boruto themselves are the most essential characters. But Sasuke can also be a great addition. His relationship with Naruto is well - known, and his skills and experience can add depth to the story. He could act as a mentor to Boruto as well.
For a more unique take, including Jiraiya could be great. His pervy but knowledgeable personality could lead to some humorous and yet useful moments. He might have some ancient knowledge about the connection between the Naruto world and the Pokémon world where Darkrai comes from. On the Pokémon side, Cynthia could be a great addition. As one of the strongest Pokémon trainers, she could offer a different perspective on Darkrai and also help in battles against any enemies that might be using Darkrai's power for evil.