The young boys (and girls) who fought in the Battle of Berlin did not fare well. Most of them served in the Hitler Youth, Volksstrum or SS units. In some cases the Volksstrum absorbed Hitler youth units, as did the SS, otherwise the Hitler Youth would operate on its own in Youth Battalions. These units where part of the Berlin last-line of defense, lead by Artur Axmann.

The children that had come from the Hitler Youth had been mentally conditioned to fight fanatically and to not surrender, and indeed they were some of the most fanatical fighters through-out the whole battle. They were told that warfare was glamorous and heroic. They were recruited with candy and chocolates (most of them were hungry) and brainwashed easily with patriotic slogans. They were told the future rested on their soldiers, and that the Russians would not show them mercy. The youth groups fought the hardest even with little to no training, and where well known for their contribution to the battle (even though it was controversial.) In the end, the Hitler Youth fighting in Berlin took heavy casualties, most were killed by Russians, Germans or died as prisoners in Russia.

The kids who served in or with the Volksstrum had a slightly better chance of survival. The Volksstrum consisted of old men, police, firefighters, postmen, ex-soldiers, WWI vets and invalids. Here the children were met with indifference. Here morale was low. The fighters in these groups weren't stupid by any means - they knew they were meat for the grinder, in a war that was already lost. Any chance they got, they tried to fee and encouraged the children to do the same. However, the problem with this was there were SS police units that hunted down deserters (men or boys) and strung them up or shot them immediately upon discovery. An unknown number of young boys (and men) where killed by their own countryman. Many kids upon their first taste of battle broke down in the chaos, and fled...right into the hands of SS police units.

Lastly, the kids who served in SS units - they were basically screwed anyway you look at it. The SS uniform was already a death sentence if captured, and they knew that. So naturally SS soldiers fought to the death, knowing that it would come all the same. The sad thing is many boys where issued SS uniforms even if they weren't with the SS, and the Russians had no sympathy for the SS uniform no matter who wore it.

So in the end one of three things happened to the kids fighting in a around Berlin.

1. They were killed in the Russian advance.
2. They were killed by SS police units for cowardliness either for fleeing the battle or refusing to fight.
3. They were captured and killed by vengeful Russian troops, as they had no mercy for anyone wearing a German uniform, or shipped off to work camps in Russia where they either died in transit or while in labor camps.

The saddest part about this whole thing - The Berlin Defense commander Helmuth Weidling gave the order to disband the Hitler Youth, as he knew further loss of life (especially amongst children) was futile. However, Artur Axmann in the confusion of the final battle never issued the order - and thousands died in vain.

Sources:

Anthony Beevor - "Berlin The Downfall:1945"

Cornelius Ryan - "The Last Battle"