I immediately guessed why, but for a slightly different reason. Some people when driving (e.g. me) have an unfortunate habit of looking at the other lights, to

I immediately guessed why, but for a slightly different reason. Some people when driving (e.g. me) have an unfortunate habit of looking at the other lights, to anticipate the green. I thought perhaps that the kid was watching the parent's head direction. In fact I suspect that this is the real answer. Lights aren't typically that hard to see ahead, even from the back seat.