There was just this week an article in NY Times about the rising number of cases of pertussis, and this sounds like that. The poor little guy. The steamy shower might help; a humidifier in his room, or vaporizer with the mentholated solution that steams out into the air. I would insist that he be tested for pertussis, which is whooping cough, and treated for it.
I think this one will help your kids health a lot. Some of the hand made remedies also u can try at home itself.
Take 1 teaspoon of cinnamon powder and 1/4 teaspoon of pepper powder boiled it and take in a glass of water add 1 teaspoon of honey to it and drink sip by sip for effective relief from sore throat cold and cough
My kid too have this kind of cough i posted my question in chennaimoms [Dot] com, they suggest many of the ideas for this kind of cough.
best solution = cool mist humidifier and in the water add 1 tablespoon of all natural eucalyptus oil! if your a organic mom then i have alot of home remidies that are completely safe and 100% effective! send me more questions if you have any.