Legal Question in Real Estate Law in California

Parents have control of their (unemancipated) minor children. Without knowing how the truck is registered, I'd say that they have the legal right to prevent you from selling the truck. It is less clear that they would have the right to sell it and pocket the money, but even that is probably legal, although maybe unethical. The deal is that they support you, and in return, they manage and control your property, your wages, etc.