Child Having Severe Cough Causing Him To Go Purple And Gasp From Breath, Sounds Like Whooping Cough. Had Suffered From Chicken Pox. Will Physio Prove Beneficial?

My grandchildren have suffered from chicken pox . They now both have a severe cough which does not want to go away. My grandaughter (age 4) developed her first spots almost a month ago, my grandson (age 2) developed his spots a week later. The cough is none productive, causes them to go almost purple as they struggle to breathe through the episodes. My grandson seems to be worse, he coughs during the night and it sounds (almost) like whooping cough as he makes the strange noise as he breathes in during the episodes. The episodes last around a minute but can go on for longer. The children are both being given physio by me, I was taught how to clear my sons chest 26 years ago by the local hospitals physio team, as he was born with breathing difficulties which left him with scarring to both lungs and very prone to chest infections.