If your child(ren) is/are into trains, YES !!!! The CA State Train Museum has something for every age. There are Thomas tables, model trains, old cars that you can walk through, etc. But better, there are a number of "train" things to look out for in Old Sac (where the train museum is located). If you are travelling from the bay area, I would suggest taking Amtrak from Jack London Square to the museum (for parts of the ride, the train runs along the bay and the museum is a 5 minute walk from the Old Sac station). Once there, in addition to the "indoors" part of the museum, depending on the season and what trains are there, there are a number of engines, oil cars, gondola cars, etc. that the kids can climb on outside, and a working roundtable that is in use when the steam engine is running (during the summer months, a steam engine that runs along the Sacramento River).
For non-train kids, you can also make the trip worthwhile by enticing them with the small children's discovery museum just around the corner from the train museum, a horse drawn carriage ride, and during baseball season, a ride on the water taxi to catch a rivercats game (minor league baseball -- which means there is a field that the little ones can run around on while you and the older kids eat BBQ and catch the game).