The prefix “sub” (when not a colloquial for substitute, or
the famed sandwich-making chain) means below or underneath.
In this way, a sub-plot is a secondary story plot interwoven
with the primary plot.
Sub-text is what is meant by dialogue, when a character says
one thing but means another.
Good stories can have a few subplots, which serve to
enhance, foreshadow, and augment the main story. They can become the readers’
more entertaining chain of events to follow, in which case they technically
fail to be “sub” and in a way take over the story.
Subtext serves many of the same functions. This post
elaborates on subtext.
Subtext can never take over. It only hits the spot for sophisticated readers who are experienced in life’s many unsaid sayings. In stories for young readers, subtext may go over the reader’s head, but they serve to expose them to this phenomenon in life. When a character says “you never looked better,” they may be saying you rarely look good. The second character knows full well what is meant, and responds with "Your words are always beyond kind." They mean the first speaker's cruelty has been registered.
It takes life
experience to understand layered meaning.
I never worry if a reader will understand. They will or they
won’t, or they may upon re-reading sometimes many years later. A story must
hold their attention just as it is. Layers woven will communicate at the
reader’s pace.
If I heard it once, I heard it many times. “Will kids get
this?”
I suggest not to be concerned about such. The only question
is, will kids find the story enjoyable and worth reading to the end.