I don't really know the details of this 'itachi kid story'. However, if Itachi is from Naruto, when he was a kid, he had to deal with a lot of family and village pressures. His actions later in life were deeply influenced by his childhood experiences, like his decision regarding the Uchiha clan.
Kid Itachi was a prodigy in the Uchiha clan. He was extremely intelligent and showed great talent in ninjutsu from a very young age. He was quiet and often seemed to be deep in thought, different from the other boisterous kids. He was also very kind - hearted, which was a bit unusual considering the somewhat cut - throat nature of the Uchiha clan at times.
There are several key events in kid Itachi's story. Firstly, his early recognition as a prodigy within the Uchiha clan. This led to him being given special training and attention. The moment he first showed extraordinary talent in ninjutsu was a turning point as it set him on a path different from other children. His interactions with the adults in the clan, especially those involved in the clan's politics, were also important. He started to understand the undercurrents of the clan's relationship with the village. And of course, his time with Sasuke, from simple brotherly moments to more profound exchanges where he was subtly guiding Sasuke's development, are all important events in his story as a kid.
In the Naruto 'itachi kid story', Itachi was born into the Uchiha clan. As a child, he quickly showed great potential. He was exposed to the growing tensions between his clan and the Hidden Leaf Village. He had to navigate this difficult situation, and it was part of what made him into the complex character he became. He loved his brother Sasuke deeply even as a kid, and this love was a major factor in his later actions.
In Itachi yaoi fanfiction, Itachi is often depicted as a complex and mysterious character. He is usually highly intelligent and powerful, which makes him an alluring figure in romantic or relationship - based stories. His loyalty, whether it be to his family, his village, or his love interest in the yaoi context, is also a common characteristic explored.
Wonder Woman is another character that might be paired with Itachi. Her Amazonian warrior heritage and Itachi's shinobi skills can be compared and contrasted. Their different views on justice, with Wonder Woman coming from a more idealistic place and Itachi having a more pragmatic approach, can lead to some great character - driven storylines in fanfiction.
Yes, there are likely such fanfictions. Many fanfiction writers like to explore the idea of Itachi coming back to life with his memories intact. This allows for interesting character interactions, especially with Naruto. Itachi could use his wisdom and skills once again, and his relationship with Naruto could further develop in new and unexpected ways.
His character could be developed by showing his adjustment to the Fairy Tail world. He could start off as a loner, but gradually open up to the members. His backstory as a ninja could be explored further in relation to the new environment, like how his past actions affect his new relationships.