@tsarstepan,
There was an effort in the early 1950's to try to reverse the trend of having the public be afraid of the effects of nuclear weapons. The reason is clear and well documented: Military strategists wanted to ensure that there would be few if any restrictions on their use, even on American soil. They came up with scenarios such as an enemy attack in the American West with tanks rolling through California, which they'd like to repel with a tactical/battlefield nuclear weapon. Thus it was in their interest to show that civilians could live and thrive just a few miles from the blast zone. They did indeed bring in large numbers of civilian observers, including the press, as well as a full compliment of military staff. No, there weren't children freely roaming as in the fake photo at the start of this question, but not only were the non-military VIP observers in the Adirondack chairs real, there were also military observers placed even closer including directly under some of the bombs, in order to "prove" the survivability. Contrary to your assertion, these weren't "top secret military events" at this point, there was a massive public relations campaign going on, and an estimated 200,000 observers, both military and civilian, were brought in to see the show. This estimate comes from the U.S. Government National Institutes of Health:
http://www.ncbi.nlm.nih.gov/books/NBK225000/
Military observers directly underneath an exploding nuke were documented in this video, you can read more about it in the National Public Radio story at this link:
http://www.npr.org/sections/krulwich/2012/07/16/156851175/five-men-agree-to-stand-directly-under-an-exploding-nuclear-bomb
The larger military program of showing how "survivable" nuclear explosion regions are is covered in this government film:
