In this day and age, allowing a minor to enlist in the military and be sent off to war is practically impossible — especially with our modern tracking systems.
But at the start of the 20th century, an accurate method of recording individual troop movement hadn't been invented; thousands of soldiers would eventually go missing through the course of the war, many of whom were actually children.
After WWI reared its ugly head, military recruiters were paid bonuses for every man they enlisted. Countless young men, many of them orphans or just seeking adventure, would simply lie about their ages to join up.
The recruiters saw dollars signs and looked past any age issues as they wrote the coercible young boy's names down, signing them up on the spot. Many feared the thought of going off to war but thought they would look weak if they didn't take part with their friends — the ultimate peer pressure.
The idea was extremely controversial at the time, but it didn't stop the boys from volunteering as they showed up to the local recruiting offices in droves. It's estimated that 250,000 boys under the age of 18 served in the British Army alone.
Once they signed up, they were sent through some basic infantry training then whisked off the front lines.
Most famously was John Condon, an Irishman who is believed to have been the youngest combatant killed; at the age of 14, he died during a mustard gas attack in Belgium while serving in the third battalion of the Royal Irish Regiment.
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Typically, when a soldier was "confirmed" killed in the war, his family would receive word by telegram of the passing — if the proper forms were filled out, which in too many cases they weren't.
The military has improved in this aspect. Today, an officer and a chaplain would show up on the families' doorstep to deliver the dreadful news.
Fun fact: The word infantry derives from Italian word "infanteria" which means "youth, foot soldier." That is all.