We will be traveling in early August, going from Klagenfurt to Venice, two teenagers, two adults, and a toddler. We leave on a Monday and want to get to Venice by Wednesday. Where would be a good/great place to stay along the way?
You don't say your means of transportation.
The train needs 3:43 hours from Klagenfurt to Venice, so it is a rather short distance. To fill up the time as you want you have to plan some detours. This will depend on your interests, the kids, and how you will be actually travelling.
We will be traveling by car and hope to maybe stop off on a nice town somewhere for a night and a good dinner.
Any part of Slovenia fits the bill, such as around Lake Bled, or Lake Bohinj, or someplace more rural.
Kobarid, Slovenia with dinner at Hiša Franko would be very special. Voted best female chef in the world in 2017 and featured on Netflix’s Chef’s Table. If you can’t get a table there, try the little sister restaurant, Hiša Polonka, also in Kobarid. Beautiful area.
I would also recommend Slovenia. Maybe spend Tuesday night in Lake Bled, then travel to Bovec or Kobarid via the Vrsic Pass the next day. Spectacular scenery. It’s an easy drive from there to Venice.