Have you wondered why kids cough at night? The origin of cough maybe a cold or allergy but cough increases during the night and is worse from 3 am to 5 am.
The body produces natural steriods which is highest at 11 am-1 am and that is why we have energy during this time and its least during 3 am-5 am and hence it constricts the wind pipe and blocks mucous. We as adults can cough or swallow mucous and remove it from the pipe. Kids are not able to do it.
Dry Air can be another reason, as air dries it worsens the cough. So the best idea would be, is to use a humidifier or allow them to inhale steam in moderation.
Gravity is another reason as sleeping causes mucous to collect and not drain through the throat. Place two or three pillows while sleeping.
Keep bedding free from dust mites and you can use a humidifier.
A vapor rub is very useful when applied on the back, chest and feet.
Try giving cough medicine atleast 2 hours before bed as it also increases cough.
You can make herbal teas with ginger and honey, (tulsi, pepper and honey).
Try Homeopathy medicines, it works very well for kids.
As your doctor about Montelukas granules, this helps to melt mucous in the throat. Its a powder which you need to mix with water or milk and given at night. (please consult your doctor before using)