Maybe because they are probably all on hardcore stimulants?
It's well known that child soldiers are usually kidnapped but only stay with their captors because they are force-fed addictive drugs which they then become dependent on to the point were they become fully desensitized to violence, effectively making them zealous cannon fodder without mercy for the enemy.
Honestly the "funny picture" could very well be the real thing, which isn't funny at all.
After I read "A Long Way Gone" I've had a different perspective, so I may just be a little too sensitive.
http://en.wikipedia.org/wiki/Ishmael_Beah