My nephew just got over the chicken pox. If your son has chicken pox they will scab over. Two weeks later, his sister broke out in a rash as you described it, my sister-in-law thought it was chicken pox. However, the rash went away in a few days. She was perplexed. The rash appeared the next week. By process of elimination, she discoved my niece is allergic to strawberries! Good luck.