"He who does not think himself worth saving from poverty and ignorance by his own efforts, will hardly be thought worth the efforts of anybody else." -- Frederick Douglass, Self-Made Men (1872)
Then they cannot be compelled to be in the car with the smoking parent, and if they choose to be in the car with the smoking parent, it's on them.
For a similar reason, a similar "in the presence of" law should also apply to adult use of alcohol and drugs.
When the election is over and we open our eyes, it will sadly be too late to wonder what the hell just happened.