How did Ishmael and the others get drawn into being active participants in the conflict instead of refugees and civilians trying to escape?

They were basically captured by government forces and indoctrinated into child soldiers. The boys were basically brainwashed. They were given food, clothing, shelter....a sense of security. These came at the expense of their innocence and perhaps their souls. They were indoctrinated into a brutal man's war where they were merely pawns.