If its just puffy eyes and no swelling in any other body part like feet etc- you need not worry.
Mild puffiness of eyes with running nose, cough
and sneezing- can well be seen in allergy
Usual allergens are dust, pollen, smoke, strong smells, perfumes, Animal danders (hair, shed skin cells, saliva), certain fabrics etc. If the allergen can be identified, its better to avoid contact with such allergens.
But in most cases, allergen is difficult to be found out.
You may ask your doctor for medications like mild steroid
nasal sprays that will prevent such episodes.
Also its better to check the patency of the Naso-lacrimal duct- the tear duct (The tube that connects eye with nose). If its blocked, repeated redness
and puffiness of eyelids can happen.
Hope my answer helps you.
Wish your son good health.