Smoking in Cars.
Now, I don't smoke and forcing your children to breathe in second hand smoke is clearly a very poor idea, But smoking is not illegal. And your car is your car, it's yours. What might be next down the line? No smoking in your home? Where does it end?
If you keep chipping away at what people can and can't do eventually you're left with a police state. It should not be up to the government to tell people whether or not to smoke around their kids. Most parents will be aware of the dangers of second hand smoke and even though they smoke themselves they won't smoke around their children. Dandy. But to make it illegal to do so smacks of Big Brother. Also who is going to enforce this law? The Gardai? Sheeeeee-eet, they have enough to be going on with.
You cannot legislate for personal choices. Or rather you should not be able to do so. As long as smoking is legal the actions of the smoking parent should be none of the government's business.