#< basically only gonna tag that cause this is more general books rather than pjo-specific

[aroaceleovaldez]

a quick helpful reference guide:

Children's books - Target demographic is generally up to like age 10 - basically elementary school and below, for us Americans.

Middle-grade books - Target demographic is approximately middle schoolers (ages 11-15).

YA (Young Adult) - Target demographic is about 15-20ish year olds, so high schoolers and early college.

There is such thing as "upper middle-grade books" (targeted more towards the upper range of middle grade, so middle schoolers going into high school) and other such more specific intended target demographic age ranges within those groupings.

What these ranges mean is that the books differ in how they present subject matter to be appropriate to the intended audience demographic. Obviously, books geared towards younger kids are going to be shorter, use simpler language, and present concepts in ways that are easier to understand for younger children. As the target age demographic increases, the length, word choice, and presentation of topics will become more complex. The actual subject matter within the book itself is unrelated to this classification system for the most part - the books are graded on what's presumed appropriate for that age-range in terms of how children learn and their presumed literacy and reading comprehension at that age, rather than the topic itself.

Rick Riordan is a middle-grade author, and his books are usually middle-grade - including the entirety of the Riordanverse and Daughter of the Deep. The only exception is The Sun And The Star, which is loosely either upper middle-grade or YA, as Mark Oshiro is a YA author and co-authored it.