Swimmer's ear is usually caused by bacteria in the thin layer of skin that lines the canal. Infection can result from an often-moist canal.The best way to get rid of swimmer ear is to keep the ear dry. Make sure that all the water is out of the ear after showers, baths etc. There are drops that you can put in the ear that will help fight the moisture.
its when water gets in your ear from swimming and infects the ear. what you do is go to a local pharmacy, gets some ear drops then have your son lay on the ear that does not have water in it and put ear drops in the infected ear then have him lay like the for 10 minutes and have him get up and turn is head to where the infected ear facing the floor and it should feel like warm water falling out. do this a couple times.
Trapped water in the ear. Try pouring a capful of hydrogen peroxide into the ear. When the peroxide is done bubbling let it drain out. This has always worked for me and I have surfed and swam competitively since I was a young child.