Perhaps the baby is a human baby left in the feudal era by some strange magic. Kagome, being from the modern era, has some knowledge about baby care that the others don't. She tries to raise the baby as best as she can, but there are also those who might want to use the baby for their own evil purposes, so Kagome has to protect it from them.
The baby could be an orphan from a nearby village that has been attacked. Kagome stumbles upon the baby while on her travels with Inuyasha. Since she has a big heart, she can't just leave the baby there, so she takes it with her.
Well, it could be a heartwarming story where Sesshomaru takes on the unexpected role of a protector for the baby Kagome.
Well, she could try to find a way to return him to his normal form. Maybe she'll search for some ancient magic or consult with a powerful sorcerer in the feudal era.
Well, perhaps the plot could involve the other characters having to take care of baby Kagome. Inuyasha might be really confused at first but then grow protective. Sango and Miroku could help out too, trying to figure out how to turn her back while also making sure she's safe and healthy.
One popular fanfiction with this premise could be 'Kagome's New Discovery'. It beautifully depicts Kagome's journey after finding the baby hanyou. The story focuses on her attempts to protect the baby and find a place for it in her world.
I'm not sure of a specific titled fanfiction exactly like this, but there could be many on platforms like Archive of Our Own. You can search for tags like 'Sesshomaru', 'Baby Kagome', 'Found Family' to narrow down the results. It's likely that in such a fanfiction, there would be a lot of cultural clashes as Sesshomaru is from a very different world than Kagome, which could make for some interesting plot points.
One great fanfiction where Kagome finds a baby Sesshomaru could be 'Kagome's Unexpected Discovery'. In this fic, Kagome stumbles upon a baby Sesshomaru in a forest glade. The story then delves into how she decides to take care of him, despite their previous enmity. It's a heartwarming tale of an unlikely bond forming between the two.
You could also check out some Inuyasha - centered forums. There are often threads where fans recommend their favorite fanfictions, and you might find some good ones about Kagome finding a baby hanyou. For example, the Inuyasha sub - Reddit might have some great suggestions.
Well, the story could involve Sesshomaru struggling to adapt to raising a baby, facing challenges and learning new skills along the way. There might also be moments of tenderness and growth for both of them as they form a special bond.
Perhaps the baby is of a different race than Thranduil's. This could lead to some interesting interactions within his kingdom. His people might be initially skeptical but grow to love the baby as it grows up, bringing a new sense of hope and unity to the realm.