The kids in the picture did not cause the fire, at least that's not what I gathered from that picture.
What's burning is a barricade.
I think the photographer wanted to show the "evils" of this war by showing kids running away from destruction.
But kids are kids, they are smiling and laughing because they're not scared, and the fact that they are not scared tells me that maybe they're running because the photographer TOLD them to run so he could properly stage his picture, and deliver his message.
the first idea (until the cut-paste evidence arose) i had was that the children, whether starting the fire, or simply watching it, enjoyed seeing destruction. the photographer seeing the children, took a picture (what the circumstances of their running is, does not effect me) it is the fact that they are smiling, and near destruction.