The child could also be a product of a magical experiment gone wrong. Sakura was involved in some sort of magical research, and the unexpected outcome was the birth of the child. This would lead to a story of her trying to figure out how to reverse the process or accept the new life she has to care for.
One idea could be that the child was the result of a past relationship that Sakura kept hidden due to the dangerous nature of the other person. Maybe the father was a powerful enemy who she had to defeat, and she was afraid of the child being used against her.
Another possibility is that the child was born during a time when Sakura was in a coma or lost her memory. She didn't know about the child until she regained her senses. In the fanfiction, the story could revolve around her trying to bond with the child she never knew she had.
It could completely change the relationships in the story. For example, her friends might be shocked and some might feel betrayed that she kept this a secret. It would also add a new layer of vulnerability to Sakura's character.
A possible plot is that the child is born with a unique power that neither Sasuke nor Sakura have. This power could attract the wrong kind of attention, and the child has to learn to control it while also hiding it from those who would misuse it. The story could also involve the child making friends with kids from different ninja clans and trying to bridge the gaps between the clans, just like their parents did in a way. Also, the child might have to deal with the pressure of being the heir to two very powerful ninja legacies.
Well, perhaps the child in the 'kakashi and sakura child fanfiction' gets involved in a mysterious mission that only they can solve because of their special heritage. The child could be the key to uniting two feuding ninja clans, using the influence of Kakashi and Sakura in the ninja world. Also, the story could focus on the child's relationship with their peers, who may be in awe or jealous of their powerful parents.
One idea could be that their child discovers a new, unique chakra ability. Since both Sasuke and Sakura are powerful ninjas, their genetic combination might lead to something extraordinary in their child. For example, the ability to combine Sakura's medical ninjutsu with Sasuke's Sharingan - like being able to see the internal damage of an enemy through the Sharingan and heal it instantly with a new form of medical jutsu.
Well, one possible plot twist could be that Natsu has been hiding her true gender to be able to participate in male - dominated activities like a certain guild or sport. Another could be that she's in love with a male character, but is afraid to reveal her gender in case it changes how he feels. Or perhaps she has a special power that is related to her being a girl secretly, like a unique form of magic that only female dragonslayers can possess.
One possible plot twist could be that Hermione's pureblood status was hidden to protect her from a dark wizard or an old family feud. When the truth comes out, she has to face unexpected enemies.
One possible plot twist could be that Zoro's gender is revealed at a crucial moment, causing shock among the other characters. For example, during a battle when an enemy discovers this secret and uses it to try and throw the team off balance.
A plot twist could be that the method Sakura uses to heal Kankuro has an unexpected side effect. For example, it gives him a temporary boost in his puppet - using abilities that he has to quickly learn to control.
A possible plot twist is that Naruto is actually a reincarnation of a great Jedi. He starts having strange dreams and visions of a past life as a Jedi, and these memories gradually influence his actions as a ninja. His friends might be confused or even a bit scared at first, but as he learns to control this new side of himself, they come to accept and rely on his Jedi - inspired skills in their battles against stronger foes.
One possible plot twist could be that Stiles has been a werewolf all along but has been using some sort of magic or potion to suppress his werewolf side. This could be revealed when he is put in a life - or - death situation and his true nature emerges to save the day.