Wow sorry to hear your little one gets cold sores. I get them too. And Stress does bring them on, so does citrus. I had one a few weeks ago, and was terrified of getting anywhere near DS face.
After suffering from them since I was a kid I finally got mine under control....I still get them but they used to last like a week and a half, and now only a few days since I started using Campho-Phenique, during the day, and Abreva at night. Abreva is over-the-counter but you have to ask the pharmacist for it. Ice compress helps with pain and swelling. Like I said i've had them for years, I have read EVERYTHING about them and have tried EVERY product available.
Now.....I have no idea if these things can be used on a 13 month old....The tubes say under the age of 2 ask a doctor. So check with the Doctor, or Pharmacist before you try them. I would say you could probably only put anything on him at night, so he doesn't keep touching it, and causing it to spread.
Now I would also tell the doctor that he keeps getting them. But in the mean time......Cold sores are contagious before the sore appears, so it's very important that as soon as your husband feels the tingly feeling, he NOT kiss the baby, touch his mouth, or food or bottles/cups. As soon as one of your sons sores clears up toothbrushes must be thrown out or boiled, and any toys that go into his mouth must be disinfected. I'm sure this will not be easy, but he could be reinfecting himself.
Ignore people's commets. coldsores have nothing to do with how you take care of your son, as they are certainty not caused by poor hygiene. I hope this helps. If you have anymore questions don't hesitate to ask...I think of myself as a "Coldsores expert" lol