Thanks for query,
It seems that your child is having allergic bronchitis
so may remain for long time.
You can continue any good cough
I would suggest you to go for blood report for Eosinophilia
as this condition can prolong cough and cold
for long time.
If there is high eosinophilic count then go for simple course of Di ethyl carbamazine medicine after consulting your doctor.
Avoid giving cold drinks,fried things.
Ok and bye.