Actually, don't use amonia, unless you don't have a cat yourself or a dog. Animals think it smells like them and return to it.
I have elderly two cats. One of them recently had an "old cat" problem. At Home Depot, in the floor cleaners area, they sell a big bottle of Capture brand pet "problem" cleaner. I can't remember the exact name of it, but it is a natural enzyme cleaner. You pour it into the problem area and let it soak a long time. It smells good to humans (faintly like vanilla) and the enzymes break down and get rid of the urine smell. Be sure you pour enough to soak the pad, because as the other poster mentioned, the pad is the problem. Let the Capture dry. It might take some time. Then you can use their spot cleaner (a spray bottle) and then their power (in a cannister) to remove the spotting caused by the enzyme cleaner.
This smells better than chemical cleaning, and isn't hard for you and your kids to smell all day long.