Your kids are going to love this place. You are going to love this place.
First of all, the Railway Museum in Omiya, Saitama Prefecture (just north of central Tokyo) is huge. Properly huge. Covering two massive levels, it feels as if there are two airport hangars sitting on top of each other.
Second of all, it is full of trains, real trains. From modern high-speed shinkansen bullets designed to take you to yonder in a flash, to opulent, 19th-century luxury carriages built to transport the Imperial family, the museum has it all.
Even if you're an adult, the Railway Museum is absolutely great for kids. Honestly. Aside from the fun of being able to board all of these trains, there are also room-sized dioramas with model trains zooming all about the place, and a huge play centre where your younger ones can seriously rummage about in Plarail (プラレール) toy heaven.
All the while you can be sitting in the cafe relaxing, watching your kids create their own train station rubber lunch boxes (the famous ekiben, 駅弁) at the mock train station cafe.
Outside (yes, there is an outside!) there are little train ride attractions, a carriage serving real train station lunch boxes, and even a carriage where you can board to eat your lunch box. Corny? No way. It's just fun.
While it won't take any effort, pay special attention to the steam train whistle as it goes off throughout the museum. The kids will love it.
The Railway Museum in Omiya is a great place to spend the day with the kids. If you don’t leave this place a bona fide train nerd, then relax, you never will.