A possible theme might be regret. The teen boy might feel regret for his actions that led to the spanking. This could be used to teach a moral lesson in the story. Also, it could touch on the theme of forgiveness. After the spanking, there could be a moment of forgiveness between the teen and the person who spanked him, which could be a way of showing the importance of moving forward and rebuilding relationships. However, we should also be aware that these themes are presented within the context of a rather controversial form of discipline, and many would argue that there are better ways to convey these themes without involving spanking.
Another theme could be coming - of - age. It might show the teen boy learning from the experience of being spanked. He could grow from it, realizing that his actions have consequences and starting to make better choices. It could be part of his journey towards becoming more responsible. However, it's important to note that this is a rather controversial way to depict coming - of - age, as modern society often frowns upon physical punishment. Also, there could be a theme of family power dynamics. The person doing the spanking, perhaps a parent or guardian, is asserting their authority over the teen boy. This can explore the relationship between the generations and how authority is maintained and challenged within a family unit. But again, this is a complex and often debated area, especially considering the ethical implications of physical discipline.
One possible theme could be discipline. In such stories, the act of spanking with a hairbrush might be used as a form of punishment for misbehavior. For example, if the teen boy has broken a family rule or has been disrespectful.