When our kids were little down time was tough to find. We usually had something else to do around the house after we put them down for the night. It seemed like we usually just watched TV, read the paper or some magazines.
Now that they are both teenagers we still have stuff to do but they have activities too like baseball with our son or some horse related thing for our daughter.
The good thing about them being older is they can help out now so we put them to work doing chores, the spare minutes are still minimal though.