My kids don't, but it's only because they've never asked. If they've ever asked, I'd absolutely tell them. I don't get why it should be a secret from your own kids??? I think anything that will help teach my kids about money and budgeting is good and helpful. I'm not ashamed of what we make and I think in times in which money is tight, it's good to be able to explain to kids why it is etc., and what to do when you have extra money etc.
Having said that, I never knew what my parents made growing up, but I really never asked either. I now know the ballpark of what my parents make.