Nasal Spray is just table salt in water, it is to help moisturize dry or irritated nostrils, and will make him feel better.
If your son is over 6 year old, he can try the Nasal Rinse(Wash) instead of the Nasal Spray. It works even better:
http://web.wenxuecity.com/BBSView.php?SubID=health&MsgID=151703
You can buy all the above from the Walmart, Target, Walgreens, GNC ...
Good Luck!