Isn't pertussis considered most dangerous for ages 6 months and younger?
I would just do the usual, make sure they get enough sleep, hand washing, proper diet and hydration, supplements. That way their little immune systems can hopefully handle whatever they come into contact with. I wouldn't choose to do abx as preventative. I don't even like them when they are needed tbh, but I do cave if there is an infection present.
Wouldn't pertussis be viral anyway?