"Hi Mummy," said one of my children over the phone. "Are you almost home?"
"Not yet," I said, "Still some errands to run."
"Well, I forgot my math book at school, so can you drive up there to get it?"
"Can't you call a friend for the assignment?"
"It's too much to do over the phone," the child said dolefully, and then her voice brightened. "Wait, I know! If you...