I think the main theme is likely the relationship between father and son, with the little red racing car as a medium through which they connect, share experiences, and create memories.
The main theme could be family and the bond between generations.
The main theme might be about传承 (inheritance in Chinese, meaning passing down something from one generation to another here). The father passes down his passion for the little red racing car to his son. It's not just about the car itself but also about the values, skills, and memories associated with it. The story may revolve around how this car helps to strengthen their relationship, as they work together on it, drive it, and cherish it over time. It could also be about the growth of the son under the influence of his father's love for the racing car, learning about responsibility, mechanics, and the joy of a shared hobby.