I had this on DS legs. He's got a bit of a heat rash (I think) on his belly but on the back of his legs it looked like little mozzie bites, about 6 of them, but one was a bit bigger. It had me stumped how a mozzie could bite the back of his legs lying down all night! :-k
This morning there are now 3 bigger type ones, more like patches of excema, so I'm not sure. He is as happy as larry & doesn't have a temp which I'm pretty cetain you'd get with Chicken Pox. My SIL has just gone through Chicken Pox with her two (2yrs and a 5 month old), she said they were both very whingey before they broke out and had temps.
Do you have the baby Love Book, I think they describe different types of rashes in there. They said not to be too concerned until temp shoots up, they become lethargic, vomit etc.