No actually, the Marauders and Co. are not child soldiers. Harry was, Draco and Regulus fate were inspired by Hitler youth (don't know how to say it in English sorry) but the Marauders? They were adults by 17 in the wizarding community, a society were adulthood goes REALLY fast: you usually marry your highschool sweetheart, there doesn't seem to be higher education after graduation...
Plus, James and Sirius were considered to be extremely powerful and talented, Remus was obviously really smart and his implication in the war was so personnal it only made sense he would be part of it (you could argue he's the only one who might have been part of some Dumbledore's plan but it would be much grayer than that: enrolling a werewolf at school could have been out of pure sympathy and feeling of justice or it could be to use him and have a werewolf by your side and in your pocket; or it could be both.), Peter was also, and despite what the narrative paints him as, definitely powerful once he was given instructions, Lily is seen as a talented in potions and able to cast powerful spells, Severus was literally a potion master by the time he hit 16 years old.
Marlene age was unknown, Dorcas as well.
It was clear that Harry being used as a pawn made Dumbledore uncomfortable and guilty while being made for the greater good. It would not have half the impact is he was used to this.
Why would he turned out the help of so many talented ADULTS? He HELPED Lily and James and wanted to be their secret keeper? He actually was disgusted by Snape's actions? DUMBLEDORE IS NOT A VILLAIN FOLKS.
"He didn't save Regulus." Regulus was barely changing his views (if we analyze the text he probably was) when he died. He never went to Dumbledore, he would not have and obviously thought of Voldemort as an enemy but 1) the Order of Phoenix were a SECRET association. 2) bro had been endoctrinated for YEARS, he might have started to change his views but to trust someone he thought of as the enemy would have taken much more time 3) I don't think he was trustful toward anyone: his family were all ennemies by association and his most trusted companion was his house elf, someone who's literally obliged to serve him and obey him.
"He didn't save Draco." He tried. He asked Severus to protect his soul. He asked him to kill him just so that Draco wouldn't have to do it. It might have been Dumbledore's greatest action toward Draco. It saved him from being a murderer AND his own guilt to not protect his family.
Dumbledore emprisoned and fought his one true love to protect the Muggles, people that destroyed his family and made his sister's life a living hell.
Dumbledore turned down power over and over again despite being very attracted to it because he knew no man should ever have it. He continued to be a Headmaster and cared very much for the children there, especially them being happy and having fun. It's crazy how much he thought about it, but he gave his heart in making school a funny thing, letting them sing however they want, waiting until they had eaten to tell them important stuff...
He cared for their security as well, even if Hogwarts has that reputation IRL in book it was seen as 1) pretty safe, even safer that Gringotts 2) it's children books, Kids need to fight some dragons for it to be fun 3) it's not that well written sometimes 4) the Wizarding world is fucking dangerous, Hogwarts didn't do that bad tbh
I do think Dumbledore wasn't per say the best person ever, but he was a man who tried to change society. Maybe very slowly, maybe not enough, but he did his fucking best and fought against supremacy and government control.
He let Harry discovered for himself about him having to die, he let him makes his own choice. It was one kid's life, a kid he canonically loved deeply. DUMBLEDORE WAS ALWAYS UP TO SACRIFICE, he made this choice for himself and let Harry do the same. He also helped him be able to survive it and, maybe it was actually him at the end and once again, he gave Harry the choice to go back to living with his friends or dying and reunite with his family, while guiding him on the path of life ("do not pity the dead, pity the living and above all the ones that live without love" he might be talking about Voldemort or about himself, who lived without it for years, reminding Harry HE is actually loved.)
By the way he never seems to forget a student's name. He remembers them all.