H2O2 in the ears kills bacteria etc. Doctors use it all the time to sterilize. The swimmers ear your son got might have been a coincidence. Try it again and dry the ear after a few minutes to make sure there is no moisture inside. You can drain the ear by tilting the ear to your shoulder, you can use q tips very very carefully and you can massage the outer ear while tilting on to a dry towel or kleenex. Perhaps the ear retained moisture around the old wax last time.
I'm not a doc this is just my humble opinion. Hope it helps. I also answered your other post about smelling ozone.