Could be a shutter speed / shakey hand issue - the buildings over the road look in sharper focus than the last guy's head. Do you know what the shutter speed was?

Best to line them up so that they're on the same plane of focus (that is, not all at different distances from your camera.

Also, if at all possible, get the flash off the camera. It has blown out the first kid and barely touched the last in the line.

Finally - watch yer backgrounds - that green thing in bottom right is very distracting.

HTH!