Turkey and Greece- family holiday in summer?

The only way to visit Santorini from Turkey in such a short time is to fly. If that's in your budget then definitely go for it, but be advised that this means flying round-trip from Istanbul to Athens for a connecting flight. Maybe you can do that first before making your way down the Turkish coast.

I would recommend visiting the Greek Islands that are near the Turkish coast. Santorini is a delight, but in my opinion not worth the time and money in your situation. I would hop on a hydrofoil from Marmaris over to Rhodes and stay a few days to explore the island. Samos, Kos, and other islands would also be easy to plug into your itinerary. The ferries from cities in Turkey to the Greek Islands are covered here: http://www.turkeytravelplanner.com/trans/Ship/GreekIslandFerries.html

I agree with Rich that if you want to visit a Greek island, it would be much easier and more economical to choose one that's near Turkey. Santorini is spectacular but the islands of the Dodecanese have much to offer that would fascinate your children. Rhodes, for example, played a big role in the crusades. It has a Knights' Quarter, where knights lived in different sections depending on language (France, Germany, Italy, etc.) There's a great museum, and palace. If any of the children are interested in paleontology, you could spend one night on nearby Tilos and see the cave where pygmy elephant bones were discovered (I don't believe the cave is open but you can see the bones in a museum). It's a fascinating story, how the elephants got trapped on Tilos and gradually evolved in size in order to survive on the island. Or visit Kos, and take a day trip over to Nisyros, which has an active (but not erupting) volcano that you can walk around. Or, since you'll be in Kas, it's a short 2.5 kilometer ferry to the picturesque, tiny island of Kastellorizo. There's a knight's castle there, too, and turtles swimming in the bay. These are beautiful, low key islands which are well worth visiting.

I want to thank you for your information. I am so surprised by the generosity people display by taking the time to help others this way! I am now thinking that I will stay a few nights on bodrum Peninsula or at gocek/Dalyan and make a day trip to one of the smaller, more convenient greek Islands. We love learning and are quite active. We will definitely check out Kastellorizo and I am going to look into tilos-sounds fascinating! Does anyone have an opinion as to whether we should stay somewhere on bodrum Peninsula or Gocek/Dalyan? Thanks again! Wendy