You are required to tell them if any children who are living at home have a drivers license. If you don’t and you have an accident, they might be able to cancel your policy retroactively since you were committing insurance fraud.
If the child is truely an adult, you don’t need to tell them if the child is not claimed as a dependent on your taxes and doesn’t live at home. Also, they don’t charge if the child is at a dorm at a considerable distance (for a New Yorker, I believe Chicago is far enough away).
If the child doesn’t need a license to commute to work or school, why did you let him get a license?
A clever trick I discovered is for the child to get the license immediately before leaving for Israel. That’s far enough away that it doesn’t affect rate, and when they come back they have the status of a new driver who has been driving for a year (or more) without an accident — even though they haven’t driven since they left home for yeshiva.