At the end of WW2 the Soviets had run out of men. They were conscripting boys.
That's not what I read. The total population of USSR around 1940 is reported as 191.7 million. All the territories have been reclaimed by 1945, so we don't need to reduce the count for that. Total losses in the war were about 20 million. So USSR had about 170 million to draw upon. If we presume the age bounds between 20 and 50, and count only men (though many women were volunteering,) we end up with about 40 million men who could be sent to the front. It's plenty.
As I read, children were working at the factories, making ammo and weapons, and at collective farms. That would be logical. What's the point of sending a boy to the front line if he can't even lift his rifle?
Perhaps you mean the "Hitler Youth" movement. Hitler indeed trained children to be fighters, and they did fight in the ruins of Berlin - they fought to the best of their abilities, but it wasn't much.
After May of 1945 USSR had enough soldiers to keep in occupied Europe, and enough soldiers to be sent to the Far East to fight Japan in China. As you know, both of those goals were successfully achieved. In 1945 the Soviet Army was strong, experienced, and the country was on war footing, with weapons and ammo and supplies coming from factories in Siberia. Fighting *that* from across the ocean would have been suicide. Hitler failed to do so just four years earlier, even though he was prepared, and his army was at that time the best in the world, and the Red Army was not prepared at all, torn apart by internal strife.
HITLERS BOY SOLDIERS
The shocking fanaticism and reckless bravery of the Hitler Youth in battle astounded the British and Canadians who fought them. They sprang like wolves against tanks. If they were encircled or outnumbered, they fought-on until there were no survivors. Young boys, years away from their first shave, had to be shot dead by Allied soldiers, old enough, in some cases, to be their fathers. The “fearless, cruel, domineering” youth Hitler had wanted had now come of age and arrived on the battlefield with utter contempt for danger and little regard for their own lives. This soon resulted in the near destruction of the entire division.
http://www.historyplace.com/worldwar2/hitleryouth/hj-boy-soldiers.htm