Finally, when I was hospitalized, there's something respiratory therapists do. Perhaps you and your son could do it to one another. Take turns lying on your stomach with your lower body inclined, if possible. Then the other cups his/her hands slightly and claps/pats on the back in the area of the lungs -- particularly the lower portions -- for 10 minutes or so a few times a day. It's a thumping motion that isn't intended to be painful but is meant to jar the phlegm loose. You guys may or may not have the energy to do this. I dunno. But it was a regular part of the therapies they used to help me.