The Auto Train really is cool. We live in Mass, and had to bring a car down to my mother in law, who lives in Clearwater, so the Auto Train was perfect. We drove to Lorton (about 7 hours), got on the train at 3pm, and the next morning, we were in Sanford. (Clearwater is about 90 minutes from Sanford). We had a very nice dinner on the train, and sleeper cars. It's too bad that after all these years, they haven't added a couple more Auto Train stops. I highly recommend it to anyone who is thinking about it, and what a trip for kids!!
PS- it looks like about a 7 hour drive for you from Columbus to Lorton! Why not do what we did - drive to Lorton, and wake up in Sanford! You'll have your own car in Florida- no rental car fees.