For anyone in New England and those traveling here, and, especially with children, there is a very nice museum in Wenham, Massachusetts (north of Boston) which has a large gallery devoted to trains and model trains amongst other kinds of displays and galleries.
They have operating model train layouts in various scales - over 20, I believe.
We have a membership and take our grandson there about once a month and he loves it every time we visit.
Check out their website at: