Whether there's a law against smoking in your car with a minor in it will depend on where you are. There are some smaller cities that have laws against smoking with a minor in the car and then there are some small and large cities that haven't passed the law yet. This law is in the beginning stages and will probably spread and end up being pretty common in most places. Your best option is to check into your city's laws to find out if it's been passed there yet.
Of course!!!. That is a really bad example. You shouldn't smoke when a minor is present. And if you are smoking in a car, the windows have to be rolled down. Or you are going to get intoxicated by the smoke.