OK, sit down, because I'm going to tell you something really funny. In fact, you're going to roll your eyes and think I'm crazy. I don't pretend to not be crazy, by the way, so get ready! Here goes...
You know when you're standing in the kitchen for an hour in the evening cooking dinner and cleaning up after the meal? Guess what? Instead of standing there, you could be doing lunges! Or squats! Or something else, whatever that might be. Imagine this: you're making gravy (because who doesn't like gravy, right?), and you need to add water to it, so you take a cup over to the sink to get some. Instead of walking the two steps over there, why not do lunges instead? Yes, I realise it may only be two or three lunges (or perhaps only one). But is two or three better than none? You betcha.
While you're waiting for the water to boil, instead of reading a magazine, why not do some deep knee bends/squats? Yes, you can. Do one, if that's all you can do. It certainly beats standing there waiting for the water to boil, doesn't it?
What about bringing food to the table? If you bring all your food to the table so your family can get their own portions, take one bowl at a time (be sure to hold it with both hands, arms outstretched in front of you), and do lunges to the table. If you're too worried about doing all that at once, then just walk regularly, but hold the bowl out in front of you. Trust me, you will feel it.
Will you look silly? Maybe, but who's going to see you? Your kids? If you're not already being silly in front of your kids, then you need to change that. Do it sometime and see whether they notice. See if your spouse notices. Tell him/her you're tightening your tush, just for them, and see what they say. Will they laugh? Maybe. Do it for a few days in a row and see whether it does you any good. If not, then don't do it anymore. If you can feel or - better yet - see results, you've just found time to exercise!
And yes, I realise that the amount of workout you get during the time you are fixing dinner is minimal. The point isn't to make this the only workout of the day, unless you are really short on time. A little exercise is better than no exercise any day.
So tonight when you're cooking, give it a go. Think of two or three exercises you can do while walking around your kitchen (same goes for baking cookies, you know), and try to do them while you're waiting on things to simmer. Let me know if you do, I'm curious about the results for others (this works for me on occasion, and I want more feedback on it).