The iconic picture of Eddie Adams changed the perception of Vietnam War in the late 1960s. But it was preceded 25 years by this image by Esther Bubley.
Also check a very well documented collection of images and art pieces done after Saigon Execution. It's worth!
Esther Bubley, Playtime. Small Boys Watching the Woodrow Wilson High School Cadets (1943)
Eddie Adams, Saigon Execution (1968)