First you should have a firm experience about religion
Going off based on things you have read will not convince them. You can preach all you like about re birth or karma from past birth and tell all the stories , you will not be able to convince a smart modern day teenager. They are skeptical. Ask for more proof
Unless you have lived a spiritual life you will not be able to convince them because what you teach is different than your actions
This is very true especially for Hollywood or Bollywood parents.
In the final run , everyone is born with past tendencies and that will shape your beliefs. Some will believe in meditation others in mantra and others in “knowledge without experience”. just mental masturbation. Which produces nothing
In the vicinity of a divine Guru even the most atheist can be converted by his will. Such Guru are very rare
Bhavin