Did the camera's flash fire? If it did then the foreground objects (i.e. the child) where affected by it, whereas the
background being too far away was not.
This is akin to a double exposure on the same frame, one with a short exposure (the flash, which is usually pretty fast) and one with a longer one, looks like more than a second.
I must say the result looks nice anyway, even if it was not done on purpose.