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 the boy in the story goes through different situations, he grows as a person.
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.
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 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 change. Since there's a new arrival, it often brings about changes in the environment or the lives of other characters.
One possible theme is scarcity. Since there's no new land, resources on the existing land would be scarce, leading to various problems.
Another theme might be cultural exchange. If the new food comes from a different culture, the story could explore how that food brings different cultures together. People might share their traditions and stories related to that food.
One possible theme could be change. A new constitution brings about significant changes in a society, and the story might explore how individuals and groups respond to this change.
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.