Ever have a change in routine in your commute that you miss because your mind goes on autopilot? Like "Oh I was supposed to pick up the dry cleaning on the way home. Oops. Guess I'll grab it tomorrow." That's how it happens in 99% of these cases, sleep-deprived parents change their routine, normally by having the "other" parent on drop off duty for the day for some reason and their brains just skip over the change and forget about it until it's too late. There was an article a few years back (I'm thinking 7 or so, since I think my wife was still pregnant when I read it and it freaked me out thinking about it from a "there but for the grace of God go I" perspective) about the different treatment by the criminal justice system of parents that this happened to. Race played some role, but more often it was down to whether the local prosecutor was a tough on crime zealot or not.
Having said all that, at 11 months and while the parents were both at church together? Doesn't fit the normal pattern.