I think you sum it up well. In terms of writing, a good YA novel and a good kids novel will differ little if at all. For the most part kids novels tend to be shorter but that isn’t a rule. Many classic stories loved by kids are quite long, but on the whole and depending on the sort of range of audience the book is meant for they may be a little shorter. Certain concepts like those of violence and death and sex and romance are often less prevalent and generally not as detailed or explored as deeply.
A “good” novel regardless of target demographic won’t usually talk “down” to the reader and will include some ideas, concepts, words, and other aspects that are a little bit of a challenge to the average reader in the group. It will usually force a little introspection or growth and get the reader thinking.

I think one way youth fiction differs from “adult” fiction is the same in which children’s and young adult novels tend to differ- while you don’t want to talk down or treat anyone “like a kid” you also have to be mindful of the reader.
Most kids aren’t going to grab on to a tight thriller about copy right infringement in a high powered corporate setting where a marriage and career are at risk over one office workers struggle with the ethics and politics of their companies latest deal. It isn’t generally “relatable” and doesn’t generally speak to the aspirations and experiences of a younger reader. So it isn’t talking down to acknowledge that there are differences in demographics. Some struggles occur at any age, but a children’s novel or a young adult novel will generally try to speak to the things going on it that persons life or mind and do it from their perspective.

Adults and younger people deal with fears about the future, losses like divorce or death, or not getting what they want. For most kids romance and sex are often not of great personal interest beyond perhaps a curiosity and hopefully not something they have experienced . For young adults they may have some experience and a stronger curiosity and a personal interest. Another universal one in literature are things like power fantasies or works dealing with the feeling of powerlessness. Different age groups tend to experience these things a little differently. Children tend to be very powerless, they generally have little autonomy or control in life but they also (hopefully) have few responsibilities and life is less complex. That isn’t to say they don’t have stress, generally their capacity for dealing with things is lower so they still can have full plates. Young adults tend to have experience or start experiencing more adult responsibilities and stresses.

They are making more decisions, dealing with more consequences, are starting to get an idea of long term thinking and a better concept of time. They are often making or on the cusp of making and facing major life choices that could have far reaching impacts.
So usually writing for these groups reflects that and it reflects the fact that for younger audiences there is much less they have probably experienced and many things they are experiencing are the first time or still pretty new. Young adults still generally have plenty of first or new experiences waiting and that they are having, but they don’t tend to be the same experiences. Older readers have more personal experience to draw off of generally and so the writing can reflect that.

So it again isn’t a rule, but it tends to be that children’s nobles often focus on protagonists who are children or who are effectively so and young adult novels tend to focus on protagonists who are young adults or who are going through things and facing things in relatable ways. Even when we read fantasy and such- we generally want to find something relatable in there. It’s either personally relatable in the characters or there are parallels to the real world. There are exceptions, but even among people who read as a form of escape or to experience what is outside their daily lives, we tend to still want to read what is relatable to us in some way, that has some anchor and relevance in our lives.

So as far as subject matter and such, there is a lot of overlap as said between general problems and issues and such between different age groups but the specifics of how they each experience them and how those things manifest is a bit different. It’s also true that while one shouldn’t talk down- there are some general bounds with things like morality. The level of nuance or moral ambiguity we can expect the audience to understand or tolerate generally differs. It’s not that kids can’t or shouldn’t see complex or gray morality- it’s that we do have to be careful in the nuances of how those things are presented because a kid generally isn’t equipped to understand something like complex romantic engagements and infidelity or intricate ethics conundrums.

One place I’ll clear this up is maybe “talking down” is poor word choice. We need to respect the audience. So it’s just a general fact that less mature or simpler minds tend to see morality in black and white. YA is much more likely to get into some “no wins” scenarios and “trolley problems” and issues where helping one person hurts another. YA is much more likely to explore “villains” and “unsavory” characters as people who perhaps want what are even reasonably or arguably good things and paint things less as black and white where right and wrong are so clearly defined. YA often deals more and dives more into overt concepts of philosophy.

But these are all broad generalizations. I think overall there is little difference and at time some novels can even be very difficult to classify. Dune is a book that is lived by adults but is a classic YA read and deals with some very heavy and very complicated themes. Lord of the Rings is heavy reading but is a YA and even Children’s literature staple. I read the hobbit at a very young age and was not able to so had it read to me. I do not recall completely understanding everything or even being able to picture much if it in my head at the time. It was very inaccessible, slow and dry for my tastes but I did like the aspects of magic and swords and such. The Sword of Truth series by Terry Goodkind can be quite heavy, dark, sexual, uncomfortable. It’s a very “adult” level read in many ways but is YA.

Piers Anthony wrote many books that straddle a line between “YA” or “Children’s” books that are still quite enjoyable I think as an adult.
So I mean… between children and YA I think if the work is good- there may be little difference and you can have a book that appeals to both groups even if some can’t completely grasp it, but there do tend to be larger differences between novels intended for the younger or less mentally developed “child” reader and the older or more mentally developed young adult reader.
The shortest way to say it is think YA tends to be more tailored to the life experiences and perspective of young adults and children‘s novels likewise to children.

You should be an English teacher yourself so good with explaining things :)

Thank you Benson. I appreciate it and hope it was of some use.

It sure was :D I learned a lot :)