The way the light changes is significant. When the moon is covered, Bette seems to have given in to her fate for what she has done, but when the moonlight shines once again, it seems to give her the strength to come up with a plan. I had never seen this opening before, now I'm intrigued to watch the rest.
The children seem to be playing in a cement cell, observed by the adults from above. The opening scene is sinister, which is what the mood I think the director was trying to portray to the viewer. He established, in the first few seconds, the unease of an entire city.