S.R.
It happened to my three year old and two days later my one year old had a microscopic blister show up on his tongue. It's extremely common to get the HSV1 virus. Most people are carriers without ever having had a cold sore. My doctor prescribed Acyclovir for my youngest to prevent a huge outbreak like his brother had. It worked wonders and nothing further developed. Since my older one had a mouth full of sores there was nothing they could do. So it was a few days on an ice cream diet for him!!! This happened over a year ago and neither one has had a single cold sore since. The Dr said it is not uncommon to go your whole life (after your initial outbreak) without ever getting another cold sore. I know it's hard to see him that way but he should feel better in a few days. Have your Dr culture the blister and that way you can get a definitive answer and not have to wonder if in fact he contracted the virus. All my best with your little one!!!