It's possible that the child is an orphan Naruto found. Naruto, having known the pain of being alone as a child, decides to take the orphan under his wing. He brings the child back to Konoha to give it a home and a family within the village.
The child could be a reincarnation of an important figure. Naruto discovers this during his travels and realizes he has to protect the child. So, he returns to Konoha with the child, hoping that together with the knowledge and power in Konoha, they can ensure the child's safety and help it fulfill its destiny.
In this fanfiction, perhaps the child is Naruto's own. Maybe he had an adventure away from Konoha and met someone special. The child could be a symbol of his growth and newfound family. He returns to Konoha with the child to introduce it to his friends and show how he has changed.
The child could be an orphan from a far - off land that Percy visited. Maybe Percy found the child alone and starving, and felt responsible for the child's well - being, so he brought the child back.
Obviously Sakura herself is the most important character. Naruto and Sasuke would also be important as they are her friends and comrades. Kakashi could also play a role, maybe as a mentor or someone who gives her advice on how to readjust to Konoha life.
One possible plot could be that Naruto has been on a long and secret mission. During this time, he met someone and had a child. Now he returns to the village with the child, and the villagers are both shocked and curious. His friends, like Sasuke, might be initially skeptical but then come to accept the new situation. The child could also have some unique powers inherited from Naruto, which could lead to various adventures as they try to figure out how to control and develop these powers.
Perhaps he is lured away by an unknown force. In some fanfictions, there might be a mysterious character or group that tricks Naruto into leaving Konoha. They could make false promises about his parents or his true power, making him curious enough to follow them.
It could be a child of one of Naruto's friends who passed away. For example, if Shikamaru died in a battle, Naruto might take in his child. Naruto would then try to pass on Shikamaru's wisdom and strategic thinking to the child, along with his own ninja skills.
It could be a rogue ninja who has been secretly building power while Naruto was away. This rogue ninja might have a vendetta against Konoha and sees Naruto's return as a challenge to his plans. So he directly confronts Naruto to prove his own strength.
Maybe some of the more conservative village elders. They have always been a bit wary of Naruto because of the Nine - Tails inside him. So they might be behind his capture in the fanfiction.
In some fanfictions, Naruto might return to Konoha to a cold reception because the villagers still hold grudges from his past. Maybe they haven't fully accepted his power or the chaos he sometimes brought. For example, they could be afraid of his Nine - Tails power flaring up again and causing destruction.
His relationship with Hinata would be complex. If the child is his and someone else's, Hinata might be hurt at first but then, because of her kind nature, she would probably try to accept the child. With his friends, they would see him in a new light, as a father now. Sasuke might be more protective of Naruto and the child, given their past bond. And for the younger generation like Boruto, they would look at Naruto differently, seeing him as not just the Hokage but also a family man.