Extending base class and using the feature without altering the derived classes

I have a C++ Base class with some derived classes. If I later extend the base class by inheritance, it there way to reflect the changes in the already derived classes. To make my question more clear, consider the following code.

#include <iostream>

class FourWheelVehicle
{
    public:
        FourWheelVehicle()
        {std::cout<<"FourWheelVehicle created\n";}
};
class Car: public FourWheelVehicle
{
    public:
        Car()
        {std::cout<<"Car created\n";}
};
class Toyota: public Car
{
    public:
        Toyota()
        {std::cout<<"Toyota Car created\n";}
};
class Audi: public Car
{
    public:
        Audi()
        {std::cout<<"Audi Car created\n";}
};
int main()
{
    Toyota t;
    std::cout<<"..............................\n";
    Audi a;
    return 0;
}

How can I extend FourWheelVehicle to FourWheelVehicleWithSeatBelt so that all the cars I derived earlier will get the seat belt without altering their code? I have tried the following:

           FourWheelVehicle
               /      \
              /        \
             /          \
            Car          \
            /\            \
           /  \            \
      Toyota Audi    FourWheelVehicleWithSeatBelt

class FourWheelVehicleWithSeatBelt: public FourWheelVehicle
{
    public:
        FourWheelVehicleWithSeatBelt()
        {std::cout<<"FourWheelVehicleWithSeatBelt created\n";}
};

The above scheme does not seem to work!