Re talking to the kids and worrying them, you will probably find that it does the opposite.
When I was 13 and my sister was 11 my father had to change jobs. The way that the pay worked in the jobs meant that we would be going almost three months with no main income, my father was the main breadwinner, mmy mother worked about 8 hours a week.
They sat us down and explained that although the bills etc were covered there was no money for extras and that although they would like to treat us, it simply wasnt possible. They commented later how good we were for not mithering for things like we may have done in the past when money was tight. We both said that it was because we knew the situation and understood, that when we had mithered it was because we didnt know that money was tight. My mother actually mentioned it recently when she said that she wished she had done things like I have which is always be honest with the kids. She tried to hide when things were tight when we were kids and then got angry and shouty when we wanted things that they couldnt afford. It was more worrying for us because we never knew if we were allowed to ask for something or not, never knew what mood we would get.
They were a lot more honest with us after that. We moved not long after he changed jobs and then a couple of years later the interest rates shot up, I am sure a lot of you remember the 15% rate, and they again sat us down and said that we may have to move again if they got any higher. We understood and although my sister especially was very upset, we accepted the reality of the situation.
Make it clear that their home, food etc is safe, just that extras are a bit more difficult to come by, and I think you'll find that they will actually be far more positive than you anticipate.
I say this as someone who has had to have that conversation this year and I am so proud at how they reacted :)