Wind-up cars are small toy vehicles that move when you twist a key or pull a lever to wind a spring inside. Once wound up, the energy stored in the spring is released, causing the car to zoom forward. These toys are often made of plastic or metal and come in various designs, from classic race cars to vintage models. Playing with wind-up cars is not only fun but also teaches kids about basic physics concepts like energy and motion. They can race their cars against friends or create obstacle courses, making it a great way to encourage imaginative play and develop fine motor skills.