Pertussis is a problem primarily in infants because they can get severe spasms of coughing where they don't get enough oxygen, and they can also get pneumonia or seizures as a complication. In adults Pertussis is usually just a mild illness that feels like a bad cold; however, the adults are certainly contagious and can give it to young children if they aren't protected.
In this country most children do get immunized for Pertussis. However, the last dose of the Pertussis vaccine is standardly given at age of four or five when children are entering kindergarten. For most people, that immunity to Pertussis generally goes away by the time they are about eight-ten years of age. We don't continue to immunize older children and adults for Pertussis, primarily because it doesn't cause significant illness in older children and adults.
There is very little risk of any type of serious illness in an otherwise healthy ten-year-old child. It would be rare for a ten-year-old to develop pneumonia or any other difficulties from a Pertussis infection. We give antibiotics to children who we know have Pertussis primarily in order to prevent them from spreading it to other people. The antibiotics won't really shorten the length of the illness, unless they are started right at the very beginning, and it will still take a couple of weeks for it to resolve.