I’ve tested this in the most recent version: 0.C-19954-g46467ec
This can be repeated by simply getting a NPC to equip a ranged weapon and having a zombie child come into range. Even if you set the NPC’s marksman/rifle skills to maximum they will always chose to melee instead; Not even going as far to switch to a superior melee weapon.
Notably this also happens with the Monster ‘Your Mother’, and dodge value of the monster doesn’t seem to be the cause of this; As NPCs will always choose to shoot cougars, zombie dogs and the like. They also have no problem shooting any other variant of zombie children.