How do class children send messages to inform their parents that they have chickenpox?

This can't be delayed. Chickenpox is a turning point for the immune system to mature, accompanied by high fever!

If there is no contact information of parents, you can only send the children back in person, so you must hurry.

If you really can't, go to the doctor first, and then inform the parents when they come to pick up the children, asking for medical expenses.

You can ask the person in charge of the school. Every school has its own countermeasures, which often happen.

Wish you a happy life!