Slovenia Itinerary

Assuming you'll have a rental car, you're picking it up in Slovenia and dropping it in Croatia. The cost for doing that is going to be very large. When I did something similar, I flew into Zagreb and picked up the car there and immediately drove to Ljubljana. Of course that comes with its own challenges, since you will be jet lagged, and the drive (about 2 1/2 hours) might better be avoided. But it worked for me.

I would skip Italy on this trip and add time in other places. I'd add one more day in Ljubljana for a day trip to Bled and Bohinj, and the Museum of Apiculture in Radovljica. (Alternatively, add a day or two in Bled.) And I'd add a day in Rovinj so you have plenty of time to visit the Istrian hill towns. Then maybe an extra day in Zagreb at the end.

How are you planning to get between each place? Are you renting a
car and driving the whole way? That is probably the best option, but
you'll pay a non-trivial dropoff fee to rent in Slovenia and return in Croatia.

Ljubljana to Kobarid gives you the opportunity to drive the Julian Alps/
Vrsic Pass.

Venice seems a bit out of the way and a different trip than the rest of
the itinerary. Maybe take the Italy days out, go from Kobarid to Rovinj,
and you can stop and see Skocjan Caves along the way. Also gives you
a chance to add some time in Bled in along the way - maybe one night
in Bled, one night in Kobarid?

Rovinj to Plitvice is probably a 4-5 hour drive? A bit out of the way, but
if you don't plan on getting back there anytime soon, then Plitvice is
worth the detour, but definitely hit the park first thing, then you will be
able to leave midday or early afternoon for the reasonable drive to Zagreb.

You might consider what we did.

Pick up car as leaving Ljubljana (there are at least a couple of international car rental companies right in center city and driving out was not hard).

Make circle through Slovenia for Lake Blend then into Croatia for Istria hilltowns (consider to substitute an agriturismo there for the days you had as Italy), Rovinj (parking is easy there in a big lot even overnight if you want to stay in the old town) back to Ljubljana, drop car in Ljubljana, take bus to Zagreb (we took Flixbus, think about only 2 hours and was easy to book on line in advance). The whole circle is not that far.

Fly out of Zagreb.

That means you may have to miss Plivice (or maybe you can fit in in that circle, we just didn't attempt).

Or if you are worried about crowds that time of year for example Lake Bled or Plivice you can always google "substitutes for [_____]" and there are many wonderful sights in both countries.

Enjoy the planning!

Great advice thank you! Your comments on bagging Italy this trip make alot of sense.

Yes we are planning on driving. I'm ok with the fee.

I agree with the other on leaving Venice out, if not Trieste as well. If you’re worried about crowds in popular tourist areas, then I think Venice is the last place you should end up in August. And if you put those days back towards Slovenia/Croatia it makes braving Plitvice or Bled much more palatable. If you’re looking for a spot between Kobarid and Rovinj, then maybe look at Piran versus Trieste.

Not knowing the ages of your kids, I think they would probably enjoy both Bled and Plitvice. The summer luge ride at Bled is wild. Plitvice will be challenging, but I think it’s still worth it if you do it right (go late on arrival, then 1st thing in the morning.) It’s an incredible place no one will forget.

I’m sure with a family, a car is almost always going to be your best bet. As the others have stated, beware the drop off fee.

great stuff thank you. i love the idea of adding more days in less stressful areas. This makes a ton of sense. Thank you SO much!