Nations Natural Bridge is located within minutes of Blanding, UT, off Ruins Road. To get a look at the sandstone bridge across Westwater Canyon requires a very, very short walk from your vehicle.
From the red "Nations Natural Bridge" sign, walk due west. There is no trail but there are numerous ways to drop down about 2 - 3 feet to the next "level" of the sandstone. Gaze directly across the canyon. It may take you a moment or two to see the north-south bridge because from this angle you cannot see the sky "through" it. You will only see is sandstone. You might be tempted to drop down into the canyon so that you can get a better look at (and photos of) the bridge, but it is extremely steep and it could be dangerous. As such, I would keep a tight hold on small children.
All-in-all, while the bridge is not that impressive from this vantage point, Westwater Canyon is quite pretty. You'll find singing birds and this would be a very suitable lunch spot to enjoy the views.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.