Not USAAF, but the youngest American service"man" in World War II was
Calvin Graham, a gunner onboard the USS South Dakota, who enlisted at age 12. However, if you're looking for USAAF examples, there's apparently an
organization for them:
Gilbert King wrote:
It wasn’t uncommon for boys to lie about their age in order to serve. Ray Jackson, who joined the Marines at 16 during World War II, founded the group Veterans of Underage Military Service in 1991, and it listed more than 1,200 active members, including 26 women.
(Source:
Smithsonian Magazine)
Dan Jones wrote:
I was just wondering what the Luftwaffe would have done with him if he’d have been shot down and captured and they discovered they had a fifteen-year-old kid on their hands?
So, if you want a strict "what is legally required" answer that is tricky as I doubt there were any formal treaties regarding child soldiers at the time. Article 77 of the Additional Protocols to the 1949 Geneva Conventions states that:
Additional Protocols to the 1949 Geneva Conventions wrote:
3. If, in exceptional cases, despite the provisions of paragraph 2, children who have not attained the age of fifteen years take a direct part in hostilities and fall into the power of an adverse Party, they shall continue to benefit from the special protection accorded by this Article, whether or not they are prisoners of war.
4. If arrested, detained or interned for reasons related to the armed conflict, children shall be held in quarters separate from the quarters of adults, except where families are accommodated as family units as provided in Article 75, paragraph 5.
5. The death penalty for an offence related to the armed conflict shall not be executed on persons who had not attained the age of eighteen years at the time the offence was committed.
(Source:
International Committee of the Red Cross)
You could argue that it was just codifying what was an
unwritten international norm at the time of World War II. (Keep in mind, this is what was done at Nuremburg. Many of the charges against the defendants were not
technically crimes, as they were not
specifically codified at the time.) However, given that they were adopted in 1977, it might be difficult given the amount of time that had passed in between.
Of course, the Germans willingly
broke other aspects of written international law, so they could have been equally cavalier about underage servicemen. However, I think exploiting them for propaganda value - showing the "evils" of the Allies - would is a pretty good guess as to what would have happened. Beyond that, I think it would have depended upon whether they were from the Western Allies or the Soviet Union. Jewish POWs are a good analogy. Despite all of the fears, you were actually
fairly safe as an American, British or French Jewish prisoner of war. (For those interested in the why, there's actually an
excellent paper on the subject.) Given that the Germans didn't end up killing the soldiers they had in captivity who they saw as untermenschen, I doubt they would have executed anyone they had lesser antagonisms against. As a matter of fact, I wouldn't have been surprised if the Germans ended up exchanging or repatriating them. 35,000 soldiers were exchanged during World War II including, crucially for this argument, some with "protected status".
[1] Returning "kids" back to their families could be portrayed as showing the "beneficence" of Germany and building on a contrast with the Allies. (For those who doubt that Germany cared this much about the way that the world thought they were caring for their prisoners, recall that they went so far as to set up a Potemkin village at Theresienstadt just to show the Red Cross how "well" they were being treated.
[2])
Underage Soviet POWs though? They would probably been worked to death just like any of the adults.