I haven't pulled my son out of swimming, i was told that was most likely where he caught them and that unless i was willing to remove him for 2 years there was no point.
My son has had them for about 6-8 months now. I took him to the dr who said anything you do to aggravate the area will help them go away faster. He suggested a mild acne cream which i used twice daily on him for about a week. It helped clear some up, but not all. Also he said covering them in micropore tape is really good. You leave it on overnight (min) and as when you take it off it really upsets them and then your body realises they are there and attacks. I did this once, and i think that helped more than the cream did. But i haven't done it again as it really upset my son as he couldn't understand why i did it. I found taking it off in the shower was better than taking it off dry.