Sorry to hear your children have gone down with chickenpox. But it's usually best to get it during childhood as it helps to boost immunity to the virus, whereas it can potentially cause complications if contracted during adulthood.
It should begin to clear up in around 6 days time. Hope you've got enough paracetamol at hand! (don't use Ibuprofen/nurofen as it can sometimes make them feel very ill) and Calamine cream as this is probably better than calamine lotion as it has a more moisturising effect. ---Oops sorry! I'm going into professional technical mode here, you probably know all this anyway Shorty.
Anyhow, I wish them a quick recovery, and its good to know that your tutors have been so understanding with this.