Well, it might explore the dynamic of their relationship in a really unique way. Since it mentions 'daddy' Castiel and 'baby' Dean, it could be set in an alternate universe where Dean is much younger or in a more vulnerable state. The nightmares could be a plot device to bring them closer together and show Castiel's protective side over Dean.
It could be about Castiel taking on a fatherly role for Dean. Maybe in the story, Dean has nightmares often, and Castiel is there to comfort him like a daddy would. For example, Castiel could use his angelic powers to soothe Dean's troubled mind during those nightmare - filled nights.
The theme of family or a found family could be prominent. Despite not being related by blood, Castiel acting as a daddy to Dean creates a family - like bond. Also, the theme of healing is possible. If the nightmares are a result of emotional wounds, then the story could be about how Dean heals with Castiel's help.
Castiel first wakes Dean gently from the nightmare. Then he sits with Dean and tells him stories about the great heroes in Heaven. He tells Dean that he is also a hero, and that no nightmare can ever truly harm him because Castiel will always be there to protect him. He strokes Dean's hair softly as he talks, which calms Dean down.
The baby could have the power of teleportation. Since both Dean and Castiel are involved in a world full of supernatural elements, teleportation would be a useful power. It could help the baby escape dangerous situations or quickly reach its parents when they are in trouble.
There's also 'Dean, Castiel and Baby: A New Bond'. This fanfiction focuses on how Castiel, in his new 'baby' form, starts to understand human emotions better through his interactions with Dean. It has a unique take on their relationship and is quite engaging.
One key element is the relationship dynamic. Dean is often portrayed as the protector of baby Castiel. For example, in many stories, Dean will go to great lengths to keep Castiel safe from harm.
Well, in these fanfictions, sometimes Castiel wraps baby Dean in his warm, trench - coat like a blanket. He holds Dean close to his chest and whispers soothing words in Enochian, which has a calming effect on Dean. It's a very tender moment that shows their deep bond.
One great story could be 'Dean's New Family'. In it, Dean discovers he's a baby daddy unexpectedly. He has to quickly adapt to having a child in his hunter life. He tries to balance protecting the baby from the supernatural threats he faces daily and being a good father. It shows his growth from a carefree hunter to a responsible dad.
Perhaps they are crying because they've reached a point of extreme exhaustion. After years of fighting, they realize they might not be able to keep going. Castiel, with his angelic nature but also his newfound humanity, and Dean, with all his emotional baggage, break down together, finding solace in each other's presence.
A popular fanfic portrays Castiel as Dean's constant shadow. He follows Dean everywhere, using his powers to prevent any harm from coming near. Whether it's a simple bar fight or a major supernatural battle, Castiel is there, with his wings spread wide to protect Dean.
Well, it could be about Gabriel abandoning or departing from a baby Castiel. Maybe it explores the reasons behind his leaving, like some sort of mission or a conflict that forces him to go.