just found hardwood floors under carpet
You ABSOLUTELY NEED to have a finish on the floor to protect it from dirt, moisture, and general wear, especially in a play room for the kids. Otherwise, it will very quickly look like crap and possibly even splinter, which would not be good with kids around. So, unless you are going for the white-trash-country-shack lifestyle and do not care if your kids get splinters in their feet almost every day in their play room after a month or so, make sure there is some sort of finish on the floor. You can cut corners on the refinishing process if you really do not care at all what it looks like, and just slop a finish down over what you have now without sanding or stripping, but make sure you put some sort of finish down, especially because the finish on your floor is probably 50 years old.
I seriously doubt there is no finish on it now. Especially given that it is probably 50 years old, it might just have an oil finish that was absorbed by the wood or a thin veneer finish that wore down over the years. Contrary to possible impressions, good floor finishes do NOT all just look like an obvious, thick, glossy piece of transparent plastic was laminated onto the floor. A well-done finish should protect the floor invisibly so as to not interfere with (and even enhance) the natural look of the wood. It is also unlikely that an unfinished piece of wood would be anything but rough and splintery after 50 years as a subfloor. So there probably is a residual finish on the floor, even if you do not obviously feel or see it.
As for cleaning it, the type of cleaning product depends almost entirely on the finish that is on the floor. If it is an oil finish, then you need special oil-based cleaners. If it is a polyurethane, then you can use almost any common cleaner, including even Windex. Murphy's oil soap is a safe bet for almost any finish.
[This message has been edited by Lawrence (edited December 26, 2000).]