http://www.bbc.co.uk/news/health-31310685

You'll still be able to increase their risk of ill health in your own home of course.

While in principle this is good thing, without enforcement (which means enough traffic cops) this is pretty much pointless.
I really don't see how any sort of prosecution will be possible without physically catching someone smoking red handed in their car with a kid and you would have to be pretty close to the vehicle to see that sort of detail.

More about the headline and being seen to do something than any actual liklihood things will improve.

What will they do for repeat offenders? Take the children into care?

In principal a good thing, in practice, not enforceable - and being in a smoke filled home is probably worse than being in the car - depending on how long you spend in the car each week. As a child, I spent less than half an hour a week in the car on average, our daughters probably not much more.