http://www.freerepublic.com/focus/f-news/3321275/posts
On the fourth post of the WWII+70 years it has numerous eye-witness accounts of the Hiroshima bomb from citizens. One man saw the parachutes coming down (scientific instruments) and thought they were canisters of pamphlets. He remembered them from days earlier and how they had shimmered in the sunlight as they fell to earth. “The Americans have brought us some more beautiful things.”
The warning pamphlets are a fairly new idea though - just within the last few weeks of the war. They would be dropped over a bunch of cities (say 20), and then 6-10 of those cities would be hit. The rest being options in case of weather I suppose, or to keep the enemy guessing. But by this time japan was sending up few to no fighters, and AAA fire was not a huge factor anymore either.