Perhaps the plot could involve the child being sent to the future for some reason. In this future, the ninja world has changed a great deal. The child has to find a way to get back to their own time while also dealing with the new threats and powers in this future world. Along the way, they discover secrets about their parents that they never knew before and use this knowledge to grow stronger.
One possible plot could be that Naruto and Fuu's child is born with unique abilities. Maybe the child has a combination of Naruto's jinchuriki powers and Fuu's special jutsu. The story could follow the child's journey in the ninja world, facing challenges from enemies who are after the child's power. The child might also struggle to fit in as they are different from the other kids, but with the help of their parents' friends and allies, they learn to embrace their abilities and become a great ninja.
A plot could be centered around the child being kidnapped at a young age. Naruto and Fuu then go on a desperate quest to find their child. The story could show their different parenting styles coming into play during this difficult time. As they search, they encounter old enemies and make new allies. The child, while kidnapped, manages to learn some important skills and when reunited with their parents, they are stronger and more determined to protect their family and the ninja world.