I am with MCoyRed and Humble Heart here,
Even though I can't possibly see how one could forget a child in the back seat especially if he normally drops her off every morning, there is such a thing as memory loss particularly for the elderly!
I have 3 children myself and I can't possibly forget they are in the back seat (they make too much dam noise). But there have been times when I have been so weighed down with things on my mind that I have totally forgotten appointments, etc. and twice in the last year I have pulled off without pumping my gas which I paid for
I really feel sorry for this poor grandfather. His mind must have really been going to forget his own grandaughter. We may never know what was on his mind. Let's keep him and the entire family in our prayers.