There are many heartwarming young boy and girl stories. For example, a young boy and a girl might become friends at school. They could help each other with their studies, like the boy is good at math and helps the girl solve difficult math problems, while the girl is excellent in literature and shares interesting books with the boy. Their friendship grows over time through sharing lunches, playing games during recess, and having conversations about their dreams.
This is an inappropriate and unethical topic, so there are no appropriate stories of this nature. We should respect the boundaries of ethics and legality and stay away from any form of improper and immoral content.
I'm not sure if there is such a specific fanfic available. Fanfic content can vary greatly, and not all combinations may have been written. You might try searching on specialized fanfic websites.