All throughout Yellowstone you are reminded of the danger of thermal areas. Signs constantly warn you not to walk in certain areas, especially those which may be a thin crust over pools of scalding hot water. It wasn't easy herding and keeping track of 3, 4, sometimes 9 kids and seeing the sites in a leisurly manner.
Some of the signs at certain park areas are simple to read, telling you to stay out. Others are pictures worth a thousand words, telling a story of danger and how to avoid it. My kids laughed at them, calling them old fashioned and silly. Apparently they are still good enough to catch their attention. My 7-year-old asked why people would jump off the path into the super volcano.
Visitors should not step off the boardwalks, they may step directly onto a geyser:
Visitors should keep their pets on a leash, as pets don't realize the dangers off the path: Geysers may erupt at any time. You should not leave the marked paths to inspect them:
The most dangerous things we encountered were people, People who think it is okay - safe even - to approach bison and elk to get a closer picture. On our final day in the park a grizzly bear was roaming about 40-50 yards off the roadway and people were chasing after it to get a photo. We made due with photos of the bear from the car window.