One idea could be to focus on Bardock's perspective before his fateful battle. Maybe explore his thoughts about his son Goku being sent to Earth and his own impending doom. He could have some premonitions about Goku's future role in saving the universe.
Often, Kid Goku is portrayed as the carefree and adventurous type. He's always looking for the next exciting thing to do, whether it's chasing after a strange animal or exploring a new area. He might be a bit naive in some aspects, especially when it comes to things like emotions.
There could also be a moment of self - discovery for both of them. Goku might see his past self in Kid Goku and realize how far he has come, while Kid Goku could get a glimpse of his future potential through meeting his adult self. They could share stories about their friends and enemies, like how Goku could talk about Vegeta and Frieza to Kid Goku, and Kid Goku could tell Goku about his early battles with the Red Ribbon Army.
Definitely include Bardock's last stand. His heroic yet doomed battle is a crucial part of the Saiyan lore. It could be written in great detail, with Bardock using his full power against Frieza's forces.
It's hard to say. Adult Goku has more experience and has achieved higher power levels. But Kid Goku has an unbridled potential that could make him a formidable opponent even to his adult self.
One popular storyline could be their adventures together in the mountains. They might encounter strange creatures and have to use their wits and skills to overcome difficulties. For example, they could find a lost magical item and have to return it to its rightful place.
In the fanfiction, their relationship could be one of mutual admiration. Kid Goku would look up to Future Goku for his experience and power. Future Goku, on the other hand, would be charmed by Kid Goku's innocence and raw potential. They could train together, and during this process, they would form a strong brother - like relationship.
In a fanfiction where Kid Goku meets Future Goku, one possibility is that Future Goku would be amazed at seeing his younger self. He might share some of the dark experiences he has had in the future, like the battles against powerful enemies and the losses. Kid Goku, being young and full of energy, could be inspired by Future Goku's strength and determination. Maybe he would start training even harder, eager to reach the level of his future self.
In this fanfiction, they might have an epic sparring session. Adult Goku could teach Kid Goku some new techniques, like the Instant Transmission. It would be amazing to see how Kid Goku reacts to Goku's Super Saiyan forms.
In a 'Goku vs Beerus' fanfiction, it's really hard to say who would win. It could depend on how the author wants to write it. If the author wants to show Goku's growth, Goku might win through some new transformation or power - up. But Beerus is a powerful God of Destruction, so he also has a great chance of winning.