I am 25 and have had canker sores for 18 years. everything that has worked for me has usually only worked a few times beofe the canker sore virus could build some kind of immunity to it. but here ya go. Iodine, but be careful! it's poison and if he swallows some he will get sick or worse, just paint the sore until it is stained and then rinse.also Alum a pickling spice works, but for me it just kept the sore small, just put a few granules on sore and wait until it tingles a little(not dangerous)and do it as often as necessary. also putting toothpaste directly on sore has worked, but it burns. eat bland foods,no spices, and don't talk and concentrate your mind on the sores going away, also trichloroacetic acid is supposed to work, but I know nothing about it. keep stress levels down and do not bite your tongue, you will find that whenever the skin is broken that a sore will erupt. email me if you need more help.