You and your family members will need a passport that is valid 6 months beyond your departure date. Make sure you have at least 2 blank pages in each passport for visa stamps, more if you are adding stops to other countries in your itinerary. In 2004, the South African Passport control required you to have a front and back page blank that is titled Visa. Don’t check that when you are on the airplane filling out your immigration form. Citizens from the US, Canada, UK, France, Germany and Spain do not require a Visa.
Make a copy of your passport and put it in a bag that is separate from where you keep your passport. It is much easier to obtain a new passport if you have a copy of your passport. If you lose your passport, contact the US Embassy.