What an exciting plan you've got brewing, Krista!
Summer 2016 already sounds awesome. Exploring the world's top destinations as a family really can be enjoyed when you sail with Disney Cruise Line. I love having to travel through Europe on these long cruises and not have to pack & unpack multiple times. Traveling in the summer months of July and August are the warmest out there. When we sailed the Mediterranean, my kids were 5 & 7 years old. We were determined to see Europe as a family, so we chose Disney's
Family Sightseeing Port Adventures. We still ended up doing a lot of walking, so we were very glad that our walking sandals were fully broken in and very comfortable. I also planned for moisture wicking outfits, hats/visors, a mini fan and sunblock. We had a backpack and we carried a couple bottles of water.
The excursions usually last all day -- tiring yes - but absolutely fascinating! We did leave our kids at the Oceaneer Club when we visited the Vatican city. I'm so glad we did, since standing in line under the sun would have been very difficult for them (it already was for us). They really did enjoy the youth clubs for the day though, it was our 1st time to leave them onboard. I felt guilty first, but when the afternoon heat hit us -- I knew I made the right decision to keep them onboard for the day. We had a great time touring without kids that day.
We were in Greece for an Adventures by Disney trip a couple years later. That's another awesome summer destination to visit. Pick age appropriate excursions, and everyone will do just fine. Watch the temps though, since you may need to plan for changes, to prevent child & parent meltdowns :-). You & your kids will love gelato - twice a day!
No matter what you choose to do, I'm sure it'll be fun since you'll all be together. ~Dolly