We had three teens/tweens in the tow.
Everyone was impressed by Santorini. Is yours into Instagram? You guys can wear white/blue and have fun taking some fashion shots.
It was scorching hot in late July/early August - and very crowded in Santorini. We did a ship excursion to see Oia and return through Fira, but that allowed us to bypass a lot of crowd at the pier.
We tendered into Mykonos. The town is a bit of an understatement after Santorini. Just do a city walk on your own - and treat the day as half a sea day. You can still take your fashion shots. Or see if there is a Greek cooking class you can join.
I know Magic isn't visiting, but our kids had the most fun in Corfu - particularly, at the Aqualand water park. That's got to be one of the most fun water parks in the emtire Mediterranean.
The kids also loved the Myrtos beach in Kefalonia. Most of the beaches in Greece aren't sandy - rather, more 'pebbly' if that's a word. Mykonos also has some, so bring your water shoes.
If your itinerary has Dubrovnik, walk the city walls on your own. Or do a non-GoT tour if with kids. Most GoT tours don't scale the main city much and probably will draw puzzled looks from your kids. Turn on the HDR in your camera, to allow the lovely city colors to pop against the shimmering Adriatic sea.
And don't be shy to leave her behind on the ship if you have a longer itinerary. She will make good friends. Ours are still in touch with their friends who hailed from all over the world.