Croatia 1 week in July-please help with itinerary

With just one week I would stay up north. Istria has Pula with Roman ruins which are not crowded like Rome and you are free to walk around. You can even dress up as a Roman and have a picture taken. There are usually young men dressed and will play fight with your son and you can take pictures. There is also aqua-park istralandia you can check out. It opened in June of 2014; first and only one in Croatia. Rovinj has I believe has pirate ships which have entertainment and/or dinners and day trips (it’s been a few years) Google Rovinj for more ideas. Save the south for another, longer trip.

I agree with Barbara, presuming that you actually have 6 full days there excluding your arrival and departure days?

Thanks everybody for your replies.

We will have 7 full days on the ground, flights have been booked into and out of Zagreb.
Most probably we'll save Dalmatia for another trip.
We like hiking, nature views. This time we are not that much into cycling, aquariums, dolphin tours, aqua parks.
We'd love to do a boat tour as well.
My son loves mysteries, medieval festivals, pirate ships, zip lining and the outdoors classic music concerts sound amazing!
Hope to find some sandy beaches, I know they're quite rare.

Thank you very much for your time and effort.

With only 7 days in Croatia and such diverse interests, I wouldn't go any further south than Plitvice. My suggestion would be to rent a car upon arrival in Zagreb and drive straight to Plitvice for 1 night. Tour the park late afternoon if time allows and spend some additional time touring the park first thing the next morning. Drive to Krk (an island) for 2 nights and then to Istria for 3 nights. Drive to Zagreb for your last night. Zagreb is a great city, so you might consider shifting 1 night from Istria to Zagreb. Be sure to try the pizza in Zagreb. It's as good as in Italy. An itinerary like this should provide a relaxing pace with no terribly long drives.

Depending on what time you arrive in Zagreb, you might consider staying your first night there and drive to Plitvice the next morning to spend the day. Either way, leaving Plitvice, be careful not to leave the driving 'til too late that first or 2nd day in Europe as the jet lag may hit and you'll find your driver dozing off during the seemingly short distance to Istria or Krk.

Leaving Plitvice around 4 or 5pm, we only drove as far as Opatija (~ 2 hours) on our 1st full day after arrival and I was very glad I didn't have to drive any further!

I must agree with others on leaving Dalmatia for some other trip. Since you have just 7 days it's better to limit the area you want to cover. Zagreb, Plitvice lakes and Istria are a great round trip with plenty to see and do. You can check this itinerary to see how to get the most out of your trip. My personal highlights on your route are Plitvice, Rovinj and Motovun in central Istria.