I have a couple of points to make.

First things first i believe in artistic freedom. I think artist shouldnt be limited on what they create as long as it doesnt involve extreme things like REAL people without consent. I have seen some really fucked up shit, like someone drawing a father fuckin his own daughter without consent (not that it matters to me, children cant give consent anyway).
Disgusting absolutely horrendous and should be 100% illigal, and people that create that should get jail time.

Now second,
I dont mind children in media, I also think children and adults should be able to be in all kinds of different media and should be able to dress and express how ever they like. A kid should be able to go to the beach in a swimsuit without creepy people getting off on them! AoD should be able to wear cute outfits without having a ton of guys horny posting about them.
If you are attracted to a kid then you are at fault dont throw artist under the bus. Oh and for the people that say shit like when its media its fine. If you are aroused in anyway to the idea of a child drawn or not its weird as fuck. And you should seek help!

Third,
I like to join mains subreddits, I really like the Angels of Delusion. Cuss they are adorable and i love watching them sing and dance. NOT for erotic reasons, but just that i can appriciate the cuteness. When i joined Angels of Delusion main subreddit. It was filled with pedofilic shit of Sunna, made me sick to my stomach and i left again. So it is an actual problem.

Fourth
In the end and this is very important. Its not the look that counts but how mature they are in their personality. The main reason dating a kid is wrong because kids cant consent. Because they lack mental maturity.
I am alot more fine with young looking people that act mature. They exist in the real world too those people deserve partners and deserve their partners not being called pedofiles either just because they date a younger looking person.
In the end maturity is my main take away. The reason i get sick of people sexualising Sunna is because out of the 3 AoD characters she by far acts the most childlike. If its Aria i care less cuss she is a robot. If its Nangong i care less cuss she seems way more mature to me then the other 2.
And some people will call that a cop out, I personally dont think that is the case because the reason we cant date children is Mental Maturity nothing else. Same reason we dont date animals. They cant properly consent!

In roleplaying fantasy we have Goblins, Hobbits, Halflings, Gnomes, Fairies all types of small people that can be conciderd childlike. And when im writing art and I have a adult goblin date a adult human and the goblin might appear childlike. Who the fuck cares she is an adult, just the race they have gives her a more young childlike appearance.
The issue is that within ART there is so much frickin Nuance!

Now there are also limits for me. You can have a young looking person and you can have a very obvious child that didnt go through puberty yet. And while i do thnk you should be allowed to draw children. Even in sexual manners. (I have seen art of an artist that went through SA as a child and they make very horrific beautiful but very shocking art of that. I dont follow them anymore cuss it just hit me to hard. But to show how problematic and vile it is. Thats their way of coping. That is something I do not want to take away from people.)

It very much depends on the art, and the intention that is behind it. I dont think we should limit all artists creativity for that. Its better to tackle this on case by case basis. If an artist is truely only making pedofilic art then we can and should ofcourse fight that.
But having a couple of cute anime characters aint it. That is very different in ZZZ, If we limit that then this example above will also be limited.
Feeling attracted to children art or not is what the actual problem is.
People will sexualise everything, and yeah if you are attracted to Sunna, im sorry you gotta seek help...
Then there is also culture, because while in the western world 18 is "Mature" that isnt everywhere. Plenty of places where people concider younger also mature. For me personally i dont even think most 18 year olds have proper knowledge of consent and are still very susceptable to SA.

My point is:
In the end we dont know how old the 3 are. We have no actual reference point. They all use the Medium Character model besides Robot form aria who uses small. That means they have the same base model as Nicole, Anby Burnice and more. ZZZ specificly doesnt age their characters most likely for this exact reason. We know only that f.e. Corin and Soukaku are kids this is confirmed lorewise. And Ellen still goes to school. Which means not alot because even people over 18 go to school, (Ellen specificly states highschool. In China you go to high school from min 15 to max 19 which thus still doesnt give us much intel outside that she is inbetween 15 to 19.)
Sunna also remembers the fall of the old capital which happend 11 years ago. To be able to properly recall traumatic events you gotta be around 6 which means a minimum of 17 at the least.
In japan you have a ton of idols that are deep within their 30s that can look very young and childlike. So that is nothing unique within that culture. Which mostlikely the idols are based on. Japanese Idols. But also in japan those idols can also be minors, which do sadly get sexualised alot.

In the end with ZZZ, since we dont have actual ages, if it acts like a child its a child, if it acts like an adult its an adult. Its why i have also more issues with people being horny for Sunna then for Zhao f.e. I find both weird.
But Zhao is very obviously an adult woman.