Killed in Action at 13: Okinawa
A number of Japanese junior high school students in Okinawa, Japan's southernmost prefecture, were mobilized and died in action in the closing days of World War II. Details about them had been little known until the discovery of new material in November 2019. It was discovered that many of the boys were only 12 when they were sent to the front lines.
Source: "Student Soldiers that Fought in the Battle of Okinawa"