If the cold
episodes are associated with fever- then it might be due to Upper Respiratory Infection
(URI)- mostly viral. Upto 6 to 10 episodes of URI are common in kids.
Frequency will be more if your kid attends a day care or play group.
As kids grow, immunity improves and gradually the frequency will come down.
You have to be sure he gets a nutritious diet with plenty of fresh fruits, veggies, nuts, milk, eggs etc.
Teach him hand hygiene and give him the needed vaccines- including flu
How-ever if its just a cold and no fever is seen- it might due to Allergic Rhinitis
Most common allergens are dust, pollen, differences in temperature, smoke, animal danders (Hair, shed skin cells, saliva etc)
If possible try to keep him away from these allergens.
There are medications to be used during the episode and to be used to prevent such attacks.
You might speak to your doctor regarding them.
Hope my answer helps you.
Wish your son good health.