Consider this an ongoing conversation. When you first bring up the subject, your kid might be caught off guard and reluctant to engage. But once you open the door to the topic, they’ll be more inclined to talk to you about it later. If your kid is still skeptical, here are some links you can suggest so they can make up their own mind.
Surgeon General: E-Cigarettes.SurgeonGeneral.gov/
American Lung Association: Lung.org/ecigs and Lung.org/help-teens-quit.