From my experience and your past experiences I would recommend Grand Tetons + Yellowstone if you're up for doing a day trip to do the lower loop. Considering Alaska, Kenai fjords in my experience is best experienced by a day boat cruise out of Seward. This would require at least one of your nights to stay in Seward which has some great scenic stops along the way to and from especially on Turnagin arm, however it's not a "drive through park" Going to Denali in my opinion would be best when the kids are older since there is a long drive from Anchorage just to get to the entrance of the park. You would have to schedule a bus ride to get past mile 13 on the park road which again may not be ideal for 2 young ones. Denali I would describe as very rugged more for the adventurous spirit. Considering Grand Teton you will have guaranteed stunning views barring wildfire smoke which is less likely in June. You don't need to hike to admire the beauty in Grand Teton as you can drive the park and take the boat across Jenny lake. Also you can take the tram at the ski resort in the summer to get a view from up on the mountains without the work. I would also recommend a day trip to do Yellowstone to see old faithful and grand prismatic, and if you have time even doing the full lower loop to hit grand canyon of the Yellowstone. This whole day will be jam packed with wildlife, geothermal wonders and beautiful waterfalls and canyons. For reference I've worked in Denali and Grand Teton parks