Back in the late 1970’s I was the NBC (Nuclear, Biological & Chemical Warfare) officer for my USMC squadron. My instructor at NBC Officer’s School told us that his instructor was married to a Japanese woman who was a 1 year old infant hiding with her mother in a bomb shelter within one mile of Ground Zero at Hiroshima, He may have said “At Ground Zero”, but my memory is not certain.
He said that she suffered no ill effects and that their children were all healthy and normal.
I could be mistaken, but I believe that I read that most people who died at Hiroshima died from blast effects, not radiation. They died from burns, crush injuries, concussion, etc.