Is it definately not thrush? My DS got this quite a lot in the nappy area, much like you described the skin around the spots was not red, just bright red spots - we got some cream and it cleared up straight away.
Im no expert but think if it was chicken pox they would be somewhere else too on the body?? My DD was absolutely covered within 12-24 hours when she had them at 2.1.
DD2 just recovered from CP. Press the bottom of a glass against the spots. If they disappear and then come back when you release the pressure then it may well be CP. Always worth checking these things out though. My GP told me that CP is a notifiable disease so you do need to go to the docs. Or NHS 24 of course...
Is cp a notifiable disease? My surgery told me not to bother coming in!
Cp spots will blister after a few hours with little liquid filled sacs rather than pus. They can be anywhere on body including eyelids, mouth, their 'bits'. The spots will continue to appear for up to a few days. They can feel very hot and miserable for first few days too.
Don't have any experience of other rashes, I'm afraid.