Putting my piece in here, but if you think about it too long, child heroes can be seen as , you know, child soldiers. Which, uh, is not good.
Lowkey, I'm not good at putting my thoughts into words and im on mobile, so I really hope this all makes sense, but;
And also a violation of human rights, which makes it worse. Like, yeah, you can argue its heroism (which, is basically legal in dc) but if you think about it too long it gets real bad, especially when you look into certain comic issues and see what happens to certain characters, like Beast Boy, or Raven, or literally any young superhero.
The psychological issues are insane. And are documented well. Quoting the wiki on child soldiers "Child soldiers who survive armed conflict frequently develop psychiatric illness, poor literacy and numeracy, and behavioral problems such as heightened aggression, which together lead to an increased risk of unemployment and poverty in adulthood. Research in the United Kingdom has found that the enlistment and training of adolescent children, even when they are not sent to war, is often accompanied by a higher risk of suicide, stress-related mental disorders, alcohol abuse, and violent behavior."
And "Child soldiers who survive armed conflict face a markedly elevated risk of debilitating psychiatric illness, poor literacy and numeracy, and behavioural problems. Research in Palestine and Uganda, for example, has found that more than half of former child soldiers showed symptoms of post-traumatic stress disorder and nearly nine in ten in Uganda screened positive for depressed mood. Researchers in Palestine also found that children exposed to high levels of violence in armed conflict were substantially more likely than other children to exhibit aggression and anti-social behaviour."
Simply put, say a child superhero doesn't want to fight crim anymore? The damage is already done, and what will the league do? Yeah, they could offer therapy, maybe even help out with civilian life, but that doesn't take away that said child has had their innocence taken away, torn apart and stomped down. I mean, in the comic issues AND animated series we can see how badly certain situations can affect them.
An example here would be, say, Young Justice Season 1, Episode 16, "Failsafe', where the Young Justice team goes into a simulation and deals with severe trauma due to the simulation going out of control. Yes, it's a simulation, but that does not stop it being traumatising, especially seeing your friends and mentors dead!
Yes, they get therapy, but these are still children! Teenagers who are being put through simulations for battles!
Another thing, pulling from the wiki on child soldiers here again, but: "Children are targeted for their susceptibility to influence, which renders them easier to recruit and control. While some are recruited by force, others choose to join up, often to escape poverty or because they expect military life to offer a rite of passage to maturity."
Which, if we look at the Justice League mentoring young heroes or employing young heroes (who could reasonably be from poor situations, see: Jason Tood, or Dick Grayson, or Artemis) for easy labour, or to make an army. (In some cases, if I'm remembering correctly from when I used to watch Yoing Justice and Justice League Animated, there have been a few episodes where they go against the government or even caused large amounts of damage that could cause civilian deaths, or even the deaths of heroes.)
You could also take Jason Tood (a famous example here) as being forced into superheroing. Depending on the backstory you choose, or even issue, you could make it out that Jason thought that if he didn't become Robin, he'd be put out on the streets. Again, street kid that was homeless for a time, and I'm not sure about you, but I'd also probably think such a thing if I was Jason.
And I am going off on a tangent and need to get back on track because i have FEELINGS on children being shoved into superheroing/villanary and if i think about it too long, i WILL go mental and rant about the government, so I give you:
Danny realising that, yeah, that Batman, and the Justice League, is violating a lot of human rights by employing or training child superheroes. Possibly even counting as human trafficking since the definition is literally "the unlawful act of transporting or coercing people in order to benefit from their work or service, typically in the form of forced labour or sexual exploitation.'
And we all know its the former. Or it can be the second, if we go by some... problematic issues (I am eyeing that one issue with Hal Jordan dating a fellow green lantern who was an alien and was said to be the 'equivalent to a 13/14 year old'. I CAN UNDERSTAND IF IT WAS SAID THAT HER SPECIES MATURED AT A DIFFERENT AGE, (SEE, MARTIANS) BUT THEY JUST DOUBLED DOWN ON IT MAN.)
Insert Danny looking up all the legal jargon he can and going into a rabbit hole and coming to the conclusion that the Justice League is as bad as the criminals they take down. He could even come to the assumption that they are even taking down criminals to make themselves look good, so anyone who finds anything wrong with them could look bitter or crazy.
I mean it's the Justice League! They're heroes who fight for the greater good, saving us and keeping out danger! There's no way they're as bad as the villains! *I say sarcastically.*