Perhaps the kid is from a foreign land that Naruto visited during one of his missions. The kid could be an outcast in his own place because of some unique trait. Naruto, being the kind - hearted person he is, decides to adopt him. It could be that the kid has a different kind of chakra or a strange mark on his body that makes others afraid of him, but Naruto doesn't care.
It's possible that the kid is a result of some sort of time - travel or alternate reality situation. Maybe the kid is actually Naruto from a different timeline or dimension, and Naruto has to figure out how to deal with this strange situation while on his training trip.
In this fanfiction, maybe the kid has some special power that Naruto notices. So Naruto adopts the kid to protect him from those who might misuse his power. Along the way, Naruto helps the kid come to terms with his power and they form a really strong bond, facing all kinds of challenges from other villages and ninja clans.
Well, great 'kid Naruto fluff fanfiction' often includes elements of the Naruto world that are unique to his childhood. For instance, his time at the Ninja Academy. It might show his struggles with schoolwork, his eagerness to learn new jutsu, and his interactions with classmates. These details bring out the charm of his character as a kid and make the fanfiction really engaging.
Well, one unique feature is the blend of different universes. For example, in a Naruto and Harry Potter crossover, Naruto's ninja magic can be compared to the wizardry in Harry Potter. It creates a whole new set of rules and interactions.
The plot could be that a kid from a small village is kidnapped by a group of ninjas from a rival village. Naruto hears about it and sets out on a journey to save the kid. Along the way, he overcomes various obstacles and battles the kidnappers to rescue the kid and return him safely home.
In many Naruto fanfictions, Naruto might save a kid by using his ninja skills. He could use his Shadow Clone Jutsu to distract the danger, like a group of bandits attacking the kid. Then he'd swoop in and rescue the kid. Maybe he'd also use his Rasengan if there was a really tough foe, like a rogue ninja.
Well, in such a fanfiction, Naruto might learn some new and cool ninja techniques from the toads. Maybe he'll have an adventure in the toad village and make new friends among the toads.
One possible relationship could be that of a student and teacher. Naruto could learn from the toads like he does from his human sensei. Another relationship might be friendship. They could become friends and support each other in different situations.
In a fanfiction where Boruto meets Kid Naruto, there could be a lot of chaos at first. Boruto might be shocked to see a younger version of his father. Kid Naruto would probably be curious about Boruto's strange clothes and gadgets. They could end up getting into some kind of adventure together, like facing a common enemy. Maybe Boruto would show Kid Naruto some of his ninja techniques from the future, and Kid Naruto would teach Boruto some of his own unique skills that he developed during his own time as a young ninja.