Complex sentence: The Hwarang were, basically, voluntary child soldiers consisting of older children, teenagers, and young adults who came mostly from aristocratic families, and who were educated in artistic, academic, and martial fields of study.
Split into simpler sentences: The Hwarang were, basically, voluntary child soldiers consisting of older children, teenagers, and young adults. Mostly from aristocratic families, who were educated in artistic, academic, and martial fields of study.