While I'm a little biased, I've always felt the Niles Canyon Railway here in California does an excellent job at recreating that "back in the day"/"you're actually going somewhere" feel. Since the late '80s, PLA volunteers have reconstructed 10+ miles of the old SP ROW through Niles Canyon (the first leg of the old Niles Jct.-Tracy secondary main) and now run trains of ex-SP and WP Harriman cars long at a brisk 15-20MPH. The run from Niles-Sunol makes for an hour or so round trip, which seems about the perfect length before the wee ones start squirming. Overall, a unique experience and a trip back in time one might not expect to find in the middle of the San Francisco Bay Area. Check it out if you're around.