Croatia with 5 year olds!

Hi Aron! Bled should be a great choice for kids. Stay at the Savica Hotel as they cater to families and can even mind the kids if you want some adult time. Even Camping Bled is a good choice on the other side of the lake as they might get to play with other kids in the campgrounds and they always have activities on. Ljubljana has a tourist train up to the castle and a zoo, plus a big aquapark at the BTC Shopping Centre. Near the caves there is a tourist farm called Hudicevec that is a real farm so the kids can play with the animals and there is a playground and bikes for hire.
We are friends so tell them Greg and Rona sent you if you like the place! If you like fun parks, then the spa resorts at Terme Catez or Terme Olimia have pools and waterslides etc. Beaches are definitely for Croatia but Slovenia has so much to do and see. Greg and Rona

My kids LOVED Slovenia and Croatia. Plitvice is a winnerlots of short hikes in the weirdest environment. We highly recommend Predjama Castle in Slovenia. One of the best in Europe, IMHO. Nearby is the Postojna Caves. They outfit you with "hobbit cloaks" for your tour on a crazed Disneyland style train. (They don't think it's crazedthat's my description. It goes really fast and is super fun.) We also stayed at Hudicevec Tourist Farm. Highly recommended. They have a huge "family apartment" for 80E per night. Very clean, piney rooms and they feed you enormous amounts of food. This place would easily command 3 times the price in Germany.
Dubrovnik might be a good starting place. It has a cool castle feeling and you can walk all the way around the walls. You could work your way north along the coast and up into Slovenia. We rented a car and driving was no problem at all.

We took a similar trip last June over 9 days with our then 3 & 4 year old girls. They had a fantastic time. We had a vehicle since we drove from Germany. Lake Bled was amazing and we stayed at Hotel Savica so I can agree with the recommendation to stay there. It has a small playground right outside and the room was a good size. We spent lots of time walking around the lake and up to the castle. We took a morning and went to Vintgar Gorge and it was an easy but gorgeous walk. We also drove to Lake Bohinj after the gorge. Really a beautiful part of Slovenia. We missed the caves as we were short on time but did a quick stop at Predjama Castle on our way to Pula, Croatia. We rented an apartment in Banjole, just 5 mins outside Pula. Villa Elizabeta had A/C, free wifi and was just 400 meters from the beach. Make sure you bring water shoes as the beaches in Croatia are rocky ones. We spent a day in Pula and another day in Rovinj. Rovinj was beautiful and we enjoyed our time there. We drove south to Zadar, which was the highlight of the trip for me. You can find the very unique Sea Organ and Salutations to the Sun here and my girls loved them and asked to go back there many times. The small old town is on a peninsula & easy to walk around, and lots of old stuff to look at and climb on. We stayed in an residential part of town at Villa Valentina and liked it very much. You can take tours to the islands or Plitvice from Zadar if you want or find a local beach and relax there. We drove to Sibenik for half a day to admire the UNESCO church there and walk along the narrow streets of this cute town. Plitvice is just under 2 hours from Zadar and my girls had fun looking at all the fish and waterfalls. We arrived mid afternoon and spent a few hours there. I have lots of photos and more details of our trip on my blog, scrappingandtraveling.blogspot.com under the 2011 archives. Check Jul, Aug & Oct for the posts.