Perhaps it could be a character from an alternate dimension. In some fanfiction scenarios, portals open between different dimensions, and Spiderman could have had an encounter with a female character from another world, which led to the baby.
Well, perhaps in the fanfiction, Spiderman saves a woman who later turns out to be pregnant with his child. He doesn't know about it until she shows up at his doorstep with the baby. Spiderman then has to figure out how to take care of the baby. He might start using his web - slinging skills in new ways, like creating a safe web - hammock for the baby to sleep in while he's on patrol, and he has to deal with the reactions of his friends and allies, like Mary Jane or Ned.
Well, the plot could be that the baby is in a high - rise building that's on fire. Spiderman swings in, using his web to create a sort of cradle to catch the baby as it's being passed out of a window by a desperate mother. Then he safely descends the building with the baby in his arms and hands it over to the paramedics waiting below.
Well, in a fanfiction, it could be due to some sort of magic spell gone wrong. Maybe a villain was trying to defeat Spiderman in a new and unique way and accidentally turned him into a baby. Another possibility is that some strange scientific experiment in the Marvel universe backfired on him.
His identity might be at risk. If people find out that Spiderman has turned into a baby, it could expose his secret identity. Also, his friends and family would have to take on new roles. For example, Aunt May would have to be more of a caretaker than ever, and his superhero friends would need to protect him from villains who might see this as an opportunity to get rid of Spiderman once and for all.
If Spiderman and White Tiger had a baby in fanfiction, their combined powers would be quite something. Spiderman's power of sticking to walls and his spider - sense could combine with White Tiger's acrobatic and combat skills. The baby might be able to use its spider - sense not just for danger but also to anticipate an opponent's moves in combat, just like White Tiger anticipates her enemies. In terms of strength, it could have a strength level that is not just a sum of their parents' but enhanced in a new way. For instance, it could lift heavier objects than either parent by using a combination of their physical and energy - based power sources.
The baby might face identity issues. With two very different superhero parents, it would have to figure out where it stands in the superhero world. Also, it could face challenges in controlling its powers. Since the powers are a mix of different natures, it could be difficult to master them all. Another challenge could be dealing with the expectations of others, as people would expect it to be as great as its parents right from the start.
The villains might use the baby as a human shield. Spiderman would have to be really careful not to harm the baby while trying to get past the villains. He'd have to use his wits and his web - slinging skills in a very precise way to disarm the villains without putting the baby in danger.
One idea could be that the baby has some of Spider - Man's powers and Black Cat's agility. Maybe the baby gets into little adventures in the city, like accidentally web - swinging into a building under construction. And Spider - Man and Black Cat have to work together to keep the baby safe while also protecting their secret identities.
In a baby spiderman fanfic, perhaps baby Spiderman discovers his powers while playing in his crib. He starts shooting webs accidentally and gets all tangled up. His parents are confused at first, but as he grows, he starts using his powers for small acts of kindness around the neighborhood, like helping an old lady get her cat out of a tree. It's a really sweet concept that could be explored in many ways in fanfiction.