Can you tell me how to know whether your child has pertussis (whooping cough) or bad cough?

You get tested. Unfortunately, the vaccine avoiders have increased the frequency of pertussis in the us to dangerous levels. With wide vaccine use, this disease affected as few as 2500 nationwide with rare deaths in the early 90's but is now up to 30, 000 nationwide, with more than 30 deaths/yr, most in infants. A test of the secretions in your kids nose can be assessed for evidence of the pertussis.