Extracting the prisoner
You may save the prisoner only before you will extract White Mamba from Bwala ya Masa village. He is in one of the buildings in the north of the village. This place is marked on the screenshot above. You may use D-Dog to make your search even easier. Make sure that there are no teenagers wandering nearby.
Finding the Rough Diamonds
You may look for the Rough Diamonds at the very beginning of the mission. Go to the 06 Post which is close to your initial location. Avoid or stun the warriors which are close to the two green tents. In one of them (shown on the screenshot above) you will find the diamonds.
Extracting twenty children
You may prefer to complete this task while eventually replaying this mission since if you won't have the fulton upgrade which will allow you to extract the underage people. If you really want to complete this task right away you need to stun every person (preferably with the sleep ammunition) and carry them to your helicopter landing's spot. Using a car may make the entire process slightly faster.
Remember - You don't have to fulton away only the children from the main village. You may find the possible targets across the entire map.