Hi there Claire!
Your husband is a very luck man! I've heard that the Steam Train tour is so much fun! Walt Disney really loved his trains and I am sure there is a lot of great information on the tour.
Now, let's see what we can do to make your wait a little bit more enjoyable! Since your kids are a little too small to take on Splash, Thunder, and Space mountain skip those. You have wonderful options of riding the Tomorrowland® Transit Authority PeopleMover, The Many Adventures of Winnie the Pooh, Dumbo The Flying Elephant, "it's a small world", Peter Pan's Flight, Pirates of the Caribbean, and Jungle Cruise. I'm not sure if you'll be able to do them all but at least it gives you a little bit of a game plan. If the kids get restless riding the rides, you can take them to Country Bear Jamboree or to the forecourt of Cinderella's Castle to watch
Dream-Along With Mickey featuring one of my great friends Goofy!
When your husband gets finished with his tour, you can try some of the other Magical rides as well like Prince Charming Regal Carrousel, The Haunted Mansion, and Tomorrowland Speedway. I hope this helps with your planing! Thanks so much for asking the moms Panel. Have a great time at the Walt Disney world Resort!!!