Historic houses are great fun for us--we love to see how people lived, what their furniture was like, what toys they played with, what they cooked and how. The historic houses around town get high stars from me because most of the tours are around 1 hour in length. I find these houses to be great "museum starters" meaning it is a museum, but not a huge museum that will take hours to get through. I start introducing children to these historic houses usually between the ages of 5-7 years old (though a well behaved preschooler might like it too) so they get used to museums.
The Majors house is another of my favorites from childhood that I now take my child to. The only way to see the house is through guided tour. It also includes Majors' blacksmith shop, which we found very interesting.
Majors was one of the founders of the Pony Express, so there is lots of Pony Express advertisements, want-ads and such throughout, which I found very interesting.