My niece had whooping cough when she was a toddler. She wouldn't really cough but we would see her gasping for her and she would start to turn purple. It was so scary. She had to stay in the hospital for treatment and they supported her with oxygen throughout her stay. Thankfully she recovered well and has not had any problems since.
I've heard that whooping cough has been affecting more Americans since the early 2000s. I think that children need to be vaccinated for it since it is very dangerous for them.