There could be any number of reasons. What I do know is that these children are very sensitive to light. To get a good color picture you would need a proper amount of good lighting. In the beginning of the rescue operations the rescuers mistakenly brought the kids out into the daylight and they died instantly. Good B&W photos can be taken with minimal lighting, so I think this may be the reason why.

Now I found this... still can't figure out where this picture coming from...