After "Superfriends" (5 and up) and "Batman the Animated Series" and "Superman the Animated Series" (8 and up), comes "Justice League" and "Justice League Unlimited" (10 and up).
"Justice League" is about a team of superheroes - Superman, Batman, Wonder Woman, Green Lantern, The Flash, Martian Manhunter, and Hawkgirl - and their struggles in defending the Earth from threats domestic and extraterrestrial.
“Justice League Unlimited” ups the ante by featuring, aside from the Justice League regulars, a wider range of Justice League members – Zantana, Green Arrow, Captain Atom, Supergirl, and dozens more. This helps add not just diversity in powers, but in gender and race. The stories range from the sublime (in “Kid’s Stuff”, a young sorcerer wishes all adults out of the world, and Batman, Superman, Wonder Woman, and Green Lantern volunteer to become kids again to be able to set things right, and “This Little Piggy” features Wonder Woman turned into a pig by the sorceress Circe, and the terrible/funny price Batman is forced to pay to save her) to the sad (“Wake the Dead” sees the simple-minded Hulk-like villain Solomon Grundy, who gave his life in a previous episode, accidentally resurrected as a mindless, destructive, and pain wracked monster, and the hard choice his one friend has to make). It also features an ongoing subplot about the concerns the government has in regards to an army of beings with godlike powers (the JLU) who only answer to themselves. There’s some meat in the midst of the cotton candy.
The stories DO feature violent conflict (the nature of the genre) but they also feature deeper storytelling, often posing moral quandaries - which is a good thing. Someone complained about Superman being faced with the notion of killing Lex Luthor: he thought it was unSupermanlike, but the truth is kids WILL come to moral crossroads, and it's much more effective to show that, rather than pose a simple moral certainty, because life is not made of moral certainties. Showing the temptation and demonstrating your hero overcoming it is a MUCH better way to present the issue. It gives them an answer to "why not". The episodes of "A Better World”, feature an alternate universe where Luthor killed the Flash, and the Justice League take matters too much in hand, killing Luthor, and lobotomizing all of their enemies to make the world "safer"...of course they have to KEEP making the world safer, becoming the Justice Lords, and crushing freedom. They attempt to bring this same "safety" to the Justice League universe, but are stopped. It delineates the heroic line with a very visible “why not” example.
It's an issue your kids will face as they get older and read comics - there's a split amongst fans between those who like their heroes "heroic" (non-lethal, like Batman and Superman of the comics) and those who prefer to not have their moral failings challenged, who cleave more to the (lethal) lowered-expectations anti-heroes of the Marvel line of characters, like Wolverine and the Punisher. It’s also common in video games based on comics, since they are generally aimed at late teens – particularly the “Arkham” line of Batman games, and “Injustice: Gods Among Us” which take all of the characters into a much darker, lethal world, to feed the bloodthirsty tastes of modern teens and young adults.
So let’s access by category:
-EDUCATIONAL VALUE: If we’re addressing academic educational value, then no, none to speak of, though on a philosophical level, there’s some educating that goes on. When Batman quotes “Quis custodiet ipsos custodes?” - the latin for “Who watches the watchmen?” he sums up the underlying theme of the first season of Justice League Unlimited: who will protect us when those who protect us grow too powerful?
-POSITIVE MESSAGES: most of the old standards. Equality. Sometimes the best way to win a fight is to not fight at all. Learn to value our differences, not hate them. For my money, the best thing it teaches is the heroic ideal that ruled comics for so long: preserve lives, good and bad, even if it means losing your own. Use power responsibly. It’s better to lead by example, rather than force. Be servants of justice, not its arbiter (BIG one – it’s the answer to all the people who say superheroes should kill their enemies rather than arrest them).
-POSITIVE ROLE MODELS: Superman – literally powerful enough to be “beyond good and evil” – that is, not bound by the social forces that punish us for bad behavior and guilt us into good…and yet he chooses to hobble himself to do the right thing, even when it would be so simple to do otherwise. Wonder Woman – much the same story as with Superman, with the addition of being a strong female character who is respected by everyone. It can be said of most of the Justice League characters though: the will to do good. They don’t HAVE to, they choose to, and that makes all the difference in the world.
-VIOLENCE and SCARINESS: laser impacts and burns, electrocution, almost drowning, hit by bodies/rocks/cars etc, shot by any number of different kinds of guns, struck by missiles and explosives. Pummeled, kicked, punched, etc. Injuries ranging from broken bones, to abrassions, burns, black eyes, and bleeding lips, to coma. Some deaths, though always offscreen. Torture. There’s a lot of violence, but then it’s a superhero show, and it’s kind of the nature of the genre. In one episode, Green Arrow attempts to snap the aging Wildcat out of indulging in cage matches (he was an old school pugilist hero, feeling lost in the modern era of superpowered heroes) by letting him pound him to within an inch of his life – he ends up in a sling and crutches, but it worked. I actually think it’s important to see consequences for violence. It always bugged me to watch the old GI Joe cartoons where EVERYONE carried a gun, engaged in massive gunfights, and NO ONE got hurt. Plus, heroism is valueless if there isn’t a chance of injury or death. Equally, you also see attempts to avoid violence and find alternative solutions. So for the most part, the violence serves the story.
-SEX: no sex/nudity, though there are a number of romances – Green Lantern and Hawkgirl, Green Lantern and Vixen (so named because she can channel animal powers, not because she’s a “vixen”), Green Arrow and Black Canary, The Question and the Huntress, and a toyed-at romance between Batman and Wonder Woman. Some embraces and kisses, and that’s about it, so if that counts as sexy to you, caveat emptor. The character design doesn’t include any over endowed women, and costume designs are generally on par with modern athletic wear (Wonder Woman’s design is pretty much exactly the same as it has been for most of her last 40 years in comics – her trunks, if they were underwear, would be considered granny panties, and are the same cut as the ones worn by Linda Carter as Wonder Woman when she played her on TV back in the 70’s). Probably the most revealing would be Hawkgirl in JLU after giving up her costume in the wake of events at the end of the second season of Justice League, she wears a sports bra/halter and leggings – nothing particularly immodest unless you have something against bare midriffs and shoulders. For the men, the Martian Manhunter basically runs around in a pair of trunks, a crossed harness across his bare chest and a cape – though he is green and not human. After that, Hawkman and Aquaman, both topless. So, no sex by modern standards.
-LANGUAGE: no bad language to speak of.
-CONSUMERISM: while, like most cartoons, there are toys generated because of the show, the toys don’t drive the show. Shows that are driven by toys would be like GI Joe, Transformers, Pokemon and all the various “card game” based shows like Yu-Gi-Oh – where the toy is the reason for the show.
-DRINKING, DRUGS, & SMOKING: as I recall there might be a few characters – villains or neutral – who smoke, none of the heroes do. There might also be champagne/cocktails shown at places like nightclubs or receptions, but other than that, not a featured behavior, and not engaged in by the main characters.
I know it sounds like a bit much, but my son enjoyed them at 10, and we have watched the whole series a few times in the years since. It provides interesting and engaging stories for a variety of ages.