In many of these fanfictions, Kagome is portrayed as a very protective mother. Given her kind heart and her own experiences in the dangerous world of demons, she would do anything to keep her baby safe. She might use her spiritual powers in new and creative ways to protect the child.
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.
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 common theme is the exploration of cultural differences. Kagome comes from a modern human world, while Sesshomaru is from a feudal demon world. Their baby would be a unique blend of both cultures. Another theme could be the acceptance of the baby within their respective communities. There might be resistance from some, like Sesshomaru's demon clan who may have strict views on purity. Also, the growth and development of the baby, with its unique powers inherited from both parents, is often a theme. The fanfiction might show how the baby learns to control its powers and find its place in the world.
There could also be humans who are afraid of the baby's mixed heritage. They might view it as an abomination and try to get rid of it. These humans could be part of a more superstitious group that believes demons and humans should never mix.
One possible story could be that Kagome somehow finds an abandoned baby in the feudal era. Sesshomaru, being the powerful demon he is, initially shows little interest. But as Kagome tries to care for the baby on her own, Sesshomaru starts to notice her determination and kindness. Eventually, he might offer some form of protection to Kagome and the baby, perhaps out of a newfound respect for Kagome.
In fanfiction, the baby could inherit Sesshomaru's grace and strength. It could have a lithe body like him. However, it would also have Kagome's human charm. Its eyes could be a mixture of Sesshomaru's intense gold and Kagome's brown, creating a really unique and alluring look. And perhaps it would have some sort of special power that combines Sesshomaru's demon abilities, such as his speed and regeneration, with Kagome's spiritual powers.
Perhaps the baby was left behind by a group of traveling humans or demons. Sesshomaru would be reluctant to get involved at first, but Kagome's motherly instincts kick in. She takes the baby in and Sesshomaru, out of a sense of duty or perhaps an unspoken bond with Kagome, decides to help. They then embark on a journey to find the baby's family or a safe place for it. Along the way, they face challenges that test their relationship and their beliefs.
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.