I'm not sure what the "best" approach is for comics work; for most, I'd guess it's ruling things out.  On the other hand, I doubt Jack Kirby used a ruler for the last forty years of his life--but then, he was Jack Kirby.  The "best" approach is the one that yields the best results for the artist consistent with his style and the professional demands of his publisher.

I remember really struggling with simple perspective as a boy, and even in high school.  One can explore the more sophisticated aspects forever, but at a basic level, I think much of it becomes instinctive after a while.  Most of your kids who stay with art probably won't be professionals, but they may well go outside and sketch from nature/life.  When I'm doing that, I work freehand, and find that simply eyeballing the angles is usually enough to translate them successfully to the page.  Knowing about horizon lines, vanishing points, and such is mainly helpful in spotting errors and, when necessary, resorting to more formal methods to correct them.