Hello,
Chicken pox is a highly contagious disease and is spread by touch or air borne contact from an infected person. The rash of chicken pox starts as red papules(slightly raised bumps) which then turns pustular and looks like dew drops. The pustule ultimately breaks and scabs are formed. If you suspect your grandson of having chicken pox then please consult a doctor at the earliest as without examination it is very difficult confirming a diagnosis.
I hope it helps. Take care and please do keep me posted on how you are doing or if you have any additional doubts. Kind regards.