I had to explain to 4 year olds what a strike was..luckily they had lost interest halfway through my explanation as there was a fly in the room!
What a wonderful picture I have in my head of your 4 year old students, how funny they are at that age and how easily they are distracted.
moosh, I wouldn't worry about it too much. If it were a regular occurrence then I would be a little concerned, but if it was a one off I would forget about it. There was a lot of tension surrounding the strikes last week and this may have sparked an unusual reaction to your DC's question. I don't think it is a bad thing for children to be exposed to various different political views, and I am sure you will be able to temper any extreme reactions your DC has with regard to them. It could lead to a very interesting family discussion regarding the present political climate. My eldest DS is studying Government and Politics and History as two of his A levels, it gets rather heated in his lessons sometimes and he loves it. However, he is 17.