I have fond memories of watching The Parent Trap and Mary Poppins with my family when I was young. Feel good movies with fun humor.
If you specifically want pre 60's, try Duck Soup (or any Marx Brothers flick), the over the top, slapstick, zany humor was tailored for children's funny bones.
You could also try some classic Chaplin or Buster Keaton. Specifically,
The General. The stunt work alone will have your kids interested. Just make sure to tell them the difference in Stunt-work now days (wires, CG, etc.) and back then (it being, well, real)