1. Reunited 〈Pro ★〉

Talk to Kaz'tik to begin. He moves very fast, so stay close to avoid him despawning.

Talk to the child that appears to finish the quest. World of Warcraft: Mists of Pandaria 1. Reunited

Chapter 7 – At the bottom of a long ladder in the hospital trenches. Talk to Kaz'tik to begin

Chapter 4 – In the kid enemy area after the room with sleeping enemies. 1. Reunited

In the in Townlong Steppes, you must escort Kaz'tik the Manipulator:

The requires finding all 5 hidden coffins in a single playthrough:

If you are level 90+ and have a flying mount, you can simply fly directly above him. The enemy mobs will despawn without you needing to fight them.