Hhhmmmmm third-grade level philosophy primer??? Jeepers, I wouldn't know what to recommend! I don't have one of those myself....
If I may offer a suggestion: On the observation that "all of philosophy is but a recapitulation of Plato," I'd recommend reading his dialogues! The beauty of Plato is that he is not a system builder, he does not construct doctrines. He is more interested in the formulation of proper questions than he is in finding answers. His method is not to tell you what to think, but to show you where to look, and bid you to go and see for yourself. My favorites: Timaeus, Apology, Symposium, Gorgias, Critias (which features the Atlantis myth), Republic, and Laws.
There is virtually no issue in philosophy that Plato didn't originally raise in his works. Which explains the statement, "all of philosophy is but a recapitulation of Plato."
Thank you for all of your beautiful posts, dearest sister in Christ!