Chickenpox is a disease caused by a virus. Most likely, your child was around a child with chickenpox about 2 or 3 weeks before. Here's what you can expect:
The disease can spread to other people until all the sores have crusted over. Most of the time, all the sores crust over about 5 to 7 days after the rash starts. It may take 2 weeks for all of the scabs to fall off.