Historically there have always been children left orphaned, abandoned by refugees escaping famine or war in other lands, or Theocracy children born out of wedlock.
These forgotten youngsters are taken in by the temples of the Mother; some are destined to become servants or administrators, but the strongest are chosen to be sent to serve and fight for the Faith as Janissaries.
For years, they train with their weapons until their master-at-arms grants them a place in a unit.
Janissaries make up the bulk of standing Theocracy armies. Though not as revered as the Temple Guard (and seen by many of the population as low-born mavericks), these footsoldiers of the Faith are respected for their bravery.
Some Jannissary units, such as the infamous Daughters of Kalash in Sarqand and the Tarnovan Nikov Patrol are chosen from the magically adept and trained with firearms, to devastating effect on the battlefield.
The upheavals of the Cataclysm and the attacks of the Great Khan and the Lich King have caused many a great settlement and town to fall to ruin, families torn apart, and countless children and babies left orphaned or abandoned. There has, therefore, been a steady of supply of new recruits.