A theme of vulnerability could be explored. Dean being in a 'baby' state implies vulnerability, and his nightmares are another aspect of that. Castiel's role then is to help Dean deal with this vulnerability. Additionally, the theme of trust could be there. Dean has to trust Castiel to help him with his nightmares, and this trust could be a central part of their relationship in the fanfiction.
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.
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.
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.
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 possible theme is the exploration of forbidden love. Given their different natures (Dean being human and Castiel being an angel), their relationship might be seen as something that goes against the natural order in the context of the show's universe. The first kiss then becomes a bold statement against those restrictions.
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.
Family dynamics is also a big theme. How does Sam react to being an uncle? How does Castiel fit into this new family situation? And of course, how does Dean interact with the mother of the baby, if she's in the picture? These are all aspects of family dynamics that are explored.
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.
Another theme is the redemption arc for Castiel. In these fanfictions, Dean plays a crucial role in helping Castiel find his way back from any dark paths he may have tread. For example, some stories show Dean standing by Castiel during his struggles with his angelic nature.
One common theme is friendship. Their bond, whether it's a platonic friendship or something more, is often explored. Writers like to show how they support each other through tough times.
One common theme is protection. Dean, as the 'daddy' figure, is often seen protecting Sam, the 'baby prince'. This can range from protecting him from physical harm like in battles against supernatural creatures.