We've been expecting my son to come down with chicken pox ever since my daughter had it over the half term. Today will be the 16th day since her rash appeared. There has been no sign of it on my son until today when I noticed this one spot on his arm, the thing is it looks dry and crusty already? My daughter's spots came up as blisters first. Do you think this could be chicken pox or something else? The other little bumbs you can see in the pic are eczema. Thanks