Thank you for your query.
Your child got a viral illness with common cold
Some times allergy
to pollen or other allergens also lead to similar condition.
If there is nose block, you can use saline nasal drops to clear the nostrils and for easy breathing.
Oral antihistamines like chlropheniramine drops can be given which is a prescribed drug.
Therefore I advise you to consult your Pediatrician
for the examination of the child and for the medication advise.
Hope I have answered your query.