What strikes me is the formality of this. Most executions of non-combatants in the 20th Century were of two types.
“Heat of the moment” killings by troops, (the SS in Oradour-sur-Glane, France, The Germans across E. Europe, the Russians in East Prussia, Rape of Nanking)
Systemic policy killings (the Holocaust, Soviet Purges, Pogroms across E. Europe)
This one was unique. They simply tried and executed a whole family as suspected spies under the color of law. The fact that one of them was a child seems to have been irrelevant to the Japanese.