Crazy Eddie wrote:
one could make the case that Tasha Yar was hired as security chief because of her experience as a child soldier in the Turkana-IV civil wars
There's no indication that Yar was a "child soldier" at any point in her life. Her childhood story involved being a orphan street kid, caring for her younger sister, scavaging for food, and avoiding the local gangs.
Picard recuited her from another Starfleet vessel after watch her exhibit of bravery during a rescue mission.