I can't stand that sound. I love my kids, just not the sound of them running through our house, which has a crawl space. When we start building at the farm, I want to be up off the ground because my wife and I both want a nice wood deck. But we also want a concrete pad, for the sound reasons and because we want to stain it. Now, a comapny recently built a duplex near me and they built a block foundation, about two courses high, then filled with chat and then put a pad on top of it. Is it just that simple? I haven't googled it yet, because I don't know what it's called, but I'm about to try. I really like this idea, even though I know it'll cost more.
That might be a way to put in a concrete floor. That or tamping and retamping lots of gravel up the desired level.
But I wonder if a concrete floor would cut down on the noise.
It would cut down on the noise of them running through the house and jumping up and down. I would definitely tamp the chat to get it as compact as possible while still allowing some air flow. With something filling the hollow beneat hit, I don't see how a floor like that could allow much noise.
"pitter patter"...HA! Try "clomp, clomp" of little feet. It is amazing how loud my 6, 4, and 2 year olds are when running, or even walking through the house. Can't understand that you still touch the ground even if you don't try to put your feet through it I guess.
If you follow this route, don't forget to look into whatever precautions are needed for radon gas in your area.