Me either. I have to say, before I had kids, and still now that they are almost out of the house- I always check my car getting in and out. Being distracted or forgetful/oblivious isn't a crime, but when you have a baby you cannot afford to be so unobservant.
One safeguard would be to develop the habit of always putting your briefcase or pocketbook on the floor of the back seat. Then, when you get out of the vehicle at work, you would have to open the rear door to get it.
Baby still there? Surprise . . . but alive.