Talking to your children about smoking and modeling non-smoking behavior are key factors in preventing your children from starting smoking. Let them know how you feel about smoking. Kids are more comfortable knowing that there are boundaries, and they can't know the rules unless you tell them.
Kids do listen.
They may feel a need to rebel at first, but they will value the message especially coming from you. Make an emotional appeal. Telling them how hurt or disappointed you would be by their smoking has more impact than reasoning with them about the health dangers. Know that peer pressure is often used as an excuse for smoking. It may provide an opportunity to start, but kids continue to smoke for individual reasons.