How To Distinguish Chicken Pox ?

I believe my son has Chicken Pox , but someone has told me that a child he may have been in contact with has hand, foot and mouth -- how do I tell the difference? He has spots in his scalp, on his neck, in his mouth -- well pretty much all over his body. They start as a red spot, then seem to turn into blisters, and now the first ones(which appeared on sunday)have gone from being clear to cloudy? But I can t seem to find information to distinguish the two? Help please!