Step 1: Start with Reassurance
Primarily, you want to remember that children are calmed when they sense their parents taking control of a situation. This doesn't mean the parent has to have the answers but rather that parents are working together to care for the family. Of course the details of what you would say to your child will change as it relates to your life situation:
As you might already know, there have been a lot of changes in our world regarding money. This means that a lot of people are making changes in the way they spend money in order to make sure they have enough money for those things that are really needed. We are going to be making some changes in our family because we want to make sure the best way we can that we have money for the things that are most important to us. Our world has gone through some hard times before and one good thing that happens is that we really learn what it means to be a family. Spending money is never what makes us happy. It's the love we have in the family that makes us special and we're going to make sure that we always put a lot of time and energy into that.