Im 18, born in 1992. By then smoking was already relatively shunned, and from primary school me and everyone else my age were taught the dangers of smoking. Shown pictures and blasted with anti-cigarette propaganda.
I KNOW cigarettes are dangerous. Even if they were perfectly healthy I would still "Know" it, as its what me and anyone else my age has being taught. Yet people my age and under still take up smoking every day of the week, even with the warning labels on. I believe the main reason they do it, is because they are not supposed to.
As far as I can tell, the warning labels are pretty much useless. Go ahead and stick them on, as it probably does serve as some minor deterrent, however you can only protect people from themselves so much. So long as they are 18+ to buy thats the best you can do really, kids who go out of their way to get them will get ahold of them regardless.