My son is 8 years old and I believe that it's time that I teach him how to be responsible. Every night, he is assigned in putting the trash outside. Every night, he complains that I'm always making him do it and why not his younger sister who is only 4 years old. I've explained to him that he's older and that I believe that he's ready to become an adult. How can I make him do chores without complaining all the time?