It came to pass in Iraq, the known version is this: This boys were playing a futbol game in the place that is seen in the pictures. During the game they were atacked and killed by US soldiers. the reason for why they did that is unknown. Then the soldiers changed the scene adding weapons. Finally they said that they were attacked by the boys. I don't know why the soldier undressed the boy.
I read an Article in Rolling Stone called "Kill Team," about U.S. soldiers accused of murdering civilians in Iraq. It said the following:
Following the routine Army procedure required after every battlefield death, they cut off the dead boy's clothes and stripped him naked to check for identifying tattoos. Next they scanned his iris and fingerprints, using a portable biometric scanner.
I assume that they were stripping these boys for the same reason.