We took the railway with our kids to the Grand Canyon for the day and loved it. The attendant, Rob, was awesome. He was very entertaining, engaging, and made a special point of making it fun for the kids. One can tell me loved doing his job.
It is worth it to upgrade to first class. It is not that much more. The seats are comfortable and face each other. There were snacks on the way there and on the return. The train even stopped briefly on the way home so that “bandits” can board the train.
One thing to be aware of is that we had only four and a half hours before the train left for Williams. We knew this in advance and were ok with it. If anything, it worked to our advantage since it was snowing and cold, we weren’t interested in hiking or exploring too far away from the village. Something to consider is taking the train, along with your luggage, and staying a night or two in the El Tovar hotel.