C.,
I have always had issues with stinky feet, and when I finally went to a Podiatrist for help with it he said that some people's feet just sweat more and require some preventative steps.
He told me to wash my feet while in the shower with a scrubber, and exfoliate (I know feet right?). It is very important that the feet are COMPLETELY dry before socks are put on, otherwise bacteria that causes Athelete's Foot begins and can also cause stink without itch. I was instructed to try using Corn Starch Baby Powder, and a the spray below for my shoes every other day to get rid of the odor. Also, if your son is very active like one of the other poster mentioned have him carry extra socks and put the powder on at every sock change.
I know it's a lot of steps, but my Dad has stinky feet too and if he's fairly active it will just get stinkier as time goes on.
Also, Dr. Scholl's makes some inserts that help control and eliminate odor. My Podiatrist loves their stuff and he's a pediatric one. He prescribed an anti-persperant for my friends kiddo who plays basketball and that helped. Not sure if your son is at that stage...
http://www.drscholls.com/drscholls/productSearch.do?metho...
Good Luck.