We did the train from Williams to the South Rim once too. I think our kids were 11 & 13 at the time. If you plan a trip late, the train can be about the only way to stay inside the park since they seem to lock up a lot of reservations. I think the train is fun for younger kids, not sure if I’d recommend for kids older than ours were or just adults. It wasn’t bad though and we enjoyed it. It gave us the opportunity to stay inside the park which we loved. Once at the South Rim, you’re on your own until it’s time for the train to leave the next day.