Problem solved. Both the light-loving and light-averse child were satisfied with the solution of fairy lights in the lounge left on and the connecting door to the hallway left open, proof positive of something I have long suspected. If tea doesn't solve your problem, fairy lights probably will.
Both girls needed to go to the doctors at different times this afternoon. I asked Warren to take one, because I am doctored out. He came back with more antibiotics for the girl and a rose for me.
I should vacuum.