I find it almost ironic.
You shouldn't smoke around young children, but even if they wanted to, I could see it hard for a child to get ahold of a cigarette to mimic the act. I also see it as impossible that they would get support from anyone to commit the act being that they are young children and no one in their right mind is going to contribute to the child smoking just to cure curiosity.
I believe the same applies to vaping as well, but even moreso. I have a cousin-in-law that is around 8 years old ask me if he could try my GLV about two months after I started vaping. I told him, "No, kiddo. The same rules that apply to cigarettes also apply to this.". There is literally no way he can go off and vape because none exist in the family aside from me.
On the subject of second-hand smoke and vapor, yeah... I wouldn't smoke around kids. It's still unhealthy for them.
Vapor, on the other hand. While it may seed an idea that they might want to try it later in life. It's not as if they won't know about it anyway. They will learn about it at some point way before adolescence. It's also no harm to anyone, even you, the person vaping. The only harm it could do is ruin a movie if blown in plain view of the audience.
Edit: To add to this, in the future, I don't think it would be an issue for minors to vape. I can't think of any conceivable reason that any minor couldn't or shouldn't aside from nicotine consumption which by that time would be regulated anyway if we're lucky and we aren't banned.
If they really are as healthy and better for us as we preach, then it can and will do the same harm to a minor, which is none. I also see it as healthier for them and their image. Rather than standing on a street corner, ruining their lungs to pick up girls and create an image with cigarettes illegally, have them stand on a corner and promote a healthier alternative legally. No one is standing in a street yelling not to give children BB or pellet guns because it might promote domestic violence and weapon interest. I hope vaping dips into this realm in the future as well. It will be as common as chewing gum.