Hi A.,
We are in the exact same boat! My two daughter broke out with mouth sores on their tonsils and high fevers this week. They have been pretty miserable. We had to cancel our older daughter's birthday party this Sunday because our pediatrician said that she was contagious for 3-5 days. I also heard from the urgent care center where we had to take our other daughter (after doctor's hours) that it was 5-7 days. We considered just warning everyone, but decided that it was better to reschedule the party. The nurse at my doctor's office said that it is especially dangerous for both the elderly and small children. That said, we definitely cancelled our party for tomorrow because the second of my daughters just broke out on Thursday morning. I hope that your daughter feels better and that your little guy doesn't get it at all.