We have taken the AutoTrain multiple times, beginning when my 2 children were 5 and 7(they are now 21 & 23). We always traveled coach (no bedroom) without any problems. The kids enjoyed the trips. They normally put all of those traveling with children in the same car. If the train is not crowded, you will be able to spread out and use 2 seats per adult, which is more comfortable for sleeping.
Meals are included - supper consists of several selections, usually beef, fish, chicken and pasta and includes wine and dessert. Breakfast is "continental" with muffins, bagels, cream cheese, jelly, fruit, cereal, juice, milk, coffee & tea. There are also snacks provided during the evening - fruit, cookies, munchies. And a movie is shown at least 2 times during the evening in the longe car. Definately take along some games or coloring books for the kids.
We also always took a pillow and light blanket along for each person. I fold the blanket and slide inside the pillowcase to cut down on what we have to carry.
I also started sliding a sheet inside too, to put over the seat - it makes it much more comfortable for sleeping. In our carry on bag, I include a large baggie that contains a small bar of soap, wash cloth and hand towel - it makes it much easier cleaning up in the morning. Within reason, you can take along whatever you think will make traveling more comfortable.
We look at our train trip as part of the vacation, not just a means of travel. We have met some very interesting people on these trips.
Our next trip by auto train will be in October - Just DH and I this time and we are going to try a "roomette" for the first time.
Hope you enjoy your trip.
Kris