https://www.nbcbayarea.com/news/local/historic-bay-area-mode...
There's another one in the hills above Palo Alto that's open to the public once a year. Now I can't find it online. Anyone? It's not Roaring Camp.
This was a real train on private land, with a machine shop and a crew of volunteers. It had a loop of several miles.
A big part of it is funded by doing interactive Polar Express recreation trip/shows complete with singing, dancing, hot cocoa, cookies and a visit by Santa. They do two trips every day and three on weekends from before Thanksgiving to Christmas, each with several hundred passengers. It's a great experience that's pure magic for kids. The whole thing is done with top-notch production value and officially licensed by Disney. Tickets aren't cheap but well-worth the price and always sold-out with long waiting lists. When our kid was that age, getting tickets was challenging enough that we just got a yearly family membership to the museum to ensure priority selection and it became a tradition our kid still talks about every holiday. If you have (or know) kids of that age, check if there's similar holiday train excursions in your area.
We also have several smaller train clubs in the surrounding suburbs and rural areas including a couple who own and run full-sized trains on a few miles of closed track they maintain. There are also several large area parks which host clubs that run smaller "kiddie-style" trains on loops of around a half-mile. These are generally run by volunteers and free/donation. So at least in our area, I'm happy to report that train hobbies seem to be doing pretty well, although I don't know about the home-based scale train end of things.
I've ridden on the Roaring Camp Railroad, but not the Portola Valley one.