This is an amazing opportunity for kids to get value out of their readings early in their education. I know anecdotally, but there is also some research evidence, that highlighting text as a learning technique is very inefficient.
Instead, kids should learn to only write their own reaction to, reformulation of, or interpretation of a piece of text. It's not only a way for them to internalize the read material, but, for our family, it turned out to be one of the major ways to do school deliberately.
When they take notes on assigned readings, by creating their very own interpretations, questions, or reactions to them, some materials simply won't be recorded in any way because they prompt no interest in the kids. And that's fine, because they'll do less of the busywork, and more of the intentional kind. Quotes do get collected (we use the Roam+ extension for online materials) but these are almost always accompanied by their own reflections on the text.

Read Five Links Issue #002 here.