Varicella

The patient in this picture is my son, Dan, and when he was 5 he came down with chicken pox.  As you can see from the picture, he was afflicted with multiple lesions which were in different stages, showing a bit of a "mouth breather" look (from the oropharyngitis, and he is very young.  Thinking in terms of common things occurring commonly, this would be a "play the odds" kind of question, and if you did (the vast majority of you correctly identified this) you would pick chicken pox.  As you know, varicella is an airborne disease, spread primarily by droplet transmission, and is highly infectious.  Incidentally, this kid just got his first job offer from a think tank in Maryland to do some research in computational linguistics, so that is pretty cool.