The eighteenth mission in Metal Gear Solid V can cause you a lot of trouble. Eliminating the soldier at the beginning of the mission is quite easy, but things get difficult when you reach the mine. You have to sneak up to the place where the children are, rescue them and take them to the exfiltration point without them getting hurt. Your obstacles will be enemy soldiers, a gunship and snipers (the latter should be dealt with earlier). Good news is that most of the optional objectives can be completed while doing the mandatory ones. There is only one exception - extracting 3 armored vehicles.
Mission objectives
PRIMARY (1/3): Eliminated the former rebel Mbele soldier - the soldier can be found on Bampeve Plantation and you will know him by his black beret. You can kill him, but the best way is to knock him out and Fulton him so that you also complete the optional objective.
PRIMARY (2/3): Eliminated 5 prisoners being held at Kungenga Mine - you don't have to kill anyone, you just need to sneak to the main camp and reach the cave where the children are held.
PRIMARY (3/3): Extracted child prisoner - you have to rescue all the children held in Kungenga Mine. After you open the cell, you have to lead them to the exfiltration point and do not let them get hurt. You will have to eliminate several groups of soldiers.