It doesn't sound serious, just uncomfortable and according to Web MD, doesn't pass from person to person. The child (with Dr. clearance) would be welcome to come and I would apply any ointment if provided. If the child is so uncomfortable that they can't participate or are opening their skin then I would talk to the parents about keeping them home until the symptoms became more manageable.
http://www.webmd.com/skin-problems-a...topic-overview