First post!
I was watching a documentary about the Battle of Thermopylae (also known as the famous Greek Battle featuring 300 Spartans versus the Persian Army). In the first part of the documentary (between 10:30 and 18:00), there’s much talk about actual, real-life Spartan training, where training begins immediately at birth.
http://www.youtube.com/watch?v=1Q8MF6I9Tw4
Did Halsey commit war crimes by enlisting children? In this particular case, I don’t think so (based on a fictional universe). In actual life, I don’t agree. However, remember society changes and the culture of the past is not the same as the culture of the present.
I would suggest that with so many colonies in the Halo universe, there were many children abandoned or orphaned by the Covenant; thus the creation of the Spartan III program.
Clearly, based on this documentary, children who were trained from birth, tended to be successful warriors. In the documentary, it stated that if the children was “defective” the children were left to die. I think based on Halsey’s reasoning, it was better to get the “cream of the crop” rather than getting the second hand pick.
Before posting, please take a peak at that video, between 10:30 and 18:00 to fully grasp what I mean. 
Her only real war crime was kidnapping Kelly-087 in the closing days of the Human-Covenant War and luring the other Spartan-IIs except Chief to Onyx.
Quote at: 11:16
“If a baby had any imperfections at all, they wouldn’t allow it to live”
(Thus Halsey specifically choosing particular children for the Spartan II program and not worrying if the “clones” died or not)
Quote at: 11:27
“No considerations are given to the feelings of the parents, all that mattered was the benefit of the child to the state”
(Argument in Halsey’s defense)
Quote at: 12:22
“One would transform boys into efficient killing machines”
(Argument for the “Lack of Humanity” for Spartans)
Quote at: 12:27
“At age 7, every Spartan boy is taken from its family and is placed in military training camps”
(Argument in Halsey’s defense)
Quote at: 13:16
“Their education focused on military skills, discipline, and toughness”
(Argument for the "Lack of Humanity for Spartans)
Quote at: 14:10
“There seems to be indications of increasing levels of violence as you get older; one suspects that this is ultimately meant for the experience for battle”
(Argument for the "Lack of Humanity for Spartans)
Main difference is that Spartan parents seemed to consent to their children being taken for training. Whereas in the Haloverse the children had been covertly stolen from their parents.
> Main difference is that Spartan parents seemed to consent to their children being taken for training. Whereas in the Haloverse the children had been covertly stolen from their parents.
Yeah, that’s an excellent point to be made.
Again, seems “okay” with regards to the Spartan III program as those kids were already orphaned and chosen to get their revenge. Whereas the Spartan II programs seems shady based on your point made.