They might be quite surprised. Some characters like Naruto himself would probably be amused to see the different interpretations of his son's adventures in fanfiction. He might find it interesting how fans imagine Boruto's growth and the relationships within the new generation.
Naruto would likely be excited. He loves his son so much that seeing different stories about Boruto would be like seeing different potential futures for him. He might even get some inspiration from the fanfiction to give Boruto some advice in real life.
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.
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.
In the Boruto manga, Naruto unfortunately passes away. This event has a significant impact on the story and the characters. It occurs as a result of a powerful and unexpected enemy attack.
Naruto in the Boruto manga continues to be respected and influential. However, he also faces internal and external threats to the village, and his relationship with his children plays an important part in the story.