One great fanfiction with this concept is 'Baby Dean's Adventures'. It has a really cute take on how the other characters deal with a baby Dean. They struggle at first but then it becomes a heartwarming story of protection and family.
Protection is a very common theme. Since the Supernatural world is full of danger, the stories often revolve around protecting the baby from various threats like demons or other malevolent supernatural beings.
The relationship between Dean and the idea of a baby is really interesting. It shows a different side of Dean, his protective and nurturing side which we don't always see in the show.
There might be a 'baby angels supernatural fanfiction' where baby angels are being hunted by an evil entity in the supernatural realm. A group of hunters, who are used to dealing with more common supernatural beings, have to figure out how to protect these baby angels without really understanding their unique angelic nature at first.
Family is also a big theme. Despite the chaos of the supernatural world, Mary and Sam form a strong bond as mother and son. Their relationship is explored in different ways, like how Mary passes on her hunting knowledge to Sam in a way that doesn't scare him but makes him stronger. It shows how family can be a source of strength even in the face of the most dangerous and unknown supernatural elements.
You can start by looking on popular fanfiction websites such as Archive of Our Own (AO3). It has a large collection of Supernatural fanfictions, and you're likely to find many stories about Baby Lucifer there.
One great 'Baby Lucifer Supernatural Fanfiction' story could be one where Baby Lucifer is shown with a glimmer of good in him. Maybe he forms an unexpected friendship with one of the Winchester brothers, like Sam. This could lead to a series of events where he starts to question his nature as the devil.
One great Supernatural baby fanfiction is 'The Winchester Miracle'. It focuses on how the boys deal with an unexpected baby in their lives. The story is full of heartwarming moments as they learn to take care of the little one while still hunting monsters.
First, create unique and interesting baby angel characters. Give them distinct personalities, like one could be very curious and always getting into trouble because of it. Then, build a detailed supernatural world for them to exist in. For example, describe how their angelic powers work within this world.