One possible theme could be friendship, especially if the boy forms a bond with a dragon. Another might be self - discovery, as he figures out his role in the dragon - related world.
The themes in the 'dragon and boy story' can be quite diverse. Friendship is a strong one, as they overcome their initial fears or hostilities to become allies. Growth is also a theme. The boy may grow in wisdom and strength through his interactions with the dragon, and the dragon may grow in its understanding of humans. Additionally, there's the theme of discovery. Both the boy and the dragon are likely to discover new things about each other and the world around them.
One possible theme could be race. Since it's about a black boy, it might deal with issues related to race, like discrimination or the search for identity in a racially divided society.
One possible theme could be survival. If the boy is in the swamp, he has to deal with the elements and find food and shelter. Another theme might be discovery, as he could find new things about himself or the swamp environment.
One possible theme could be adaptation. Since it's about a new boy, he has to adapt to his new surroundings.
One possible theme could be growth. As it's his birthday, the boy might be getting a year older and learning new things. Another theme could be friendship, with his friends being part of the celebration.
One possible theme could be growth. As the boy in the story goes through different situations, he grows as a person.
Responsibility is surely a major theme. It could be about how the boy learns to take on different kinds of responsibilities as he grows up.
Isolation and connection. The quiet boy may initially seem isolated, but through the story, he could form deep and meaningful connections with either other characters or nature. For example, he might find a kindred spirit in an unlikely place or person. In some stories, the quiet boy may be an outcast in his community at first, but then he discovers a group that values his quiet nature, like a group of artists or thinkers who are also introverted.
One possible theme could be kindness. Since the boy is described as 'ever such a nice boy', kindness might be a central theme.
One possible theme could be friendship. The boy might form deep bonds with other characters in the story, and these friendships help him through tough times.