L.Y.
I have been to the train exhibit in Folsom and it wasn't that great. My kids are 5 and 3 and they showed zero interest. If I were you I would wait until your kids are a little older to bring them to the train museum. As for other local things to do I think you about listed them all. One thing my family likes to do is bike riding. If your daughter can ride a bike then you can stick the two younger ones in a buggy. Bring a picnic lunch and it makes for a nice activity. We also love swimming so we are constantly going to water parks or swimming pools. Another idea is to get together with other moms at a park or something for a playgroup. Parks seem to be a little bit more fun with friends around. I hope that helps!