I’m trying to nail down our itinerary and was hoping for some feedback. We are a family with kids (8, 11) looking for a mix of history, beauty and beach time. We'll be there in early June. Here’s the tentative schedule:

Days 1-2: Arrive Athens. 1 full day in Athens.
Day 3 Fly to Naxos in the am.
Days 4-6 Naxos + day trip to Delos/Mykonos
Day 7 Ferry to Santorini
Days 8-9 Santorini
Day 10 Ferry to Milos
Days 11-13 Milos
Day 14 pm flight to Athens
Day 15 Full day in Athens.
Day 16 Fly out

Main questions: Is this a good amount of island hopping that won’t be exhausting? Does the amount of days per place seem right? And lastly, if we chose not to go to Santorini, and instead flew into Milos and then ferried to Naxos, what would be a good third island to add to the itinerary that would be on the way back to Athens?

I'm not sure any of us can answer whether that's an exhausting amount of island hopping or not. You know yourselves and your children, and ultimately, you'll be a better judge than any of us,

I travel HARD and, as a solo traveler, wanted 3 days for Naxos (including a day trip to Delos) -- and my time there did NOT include any beach time. I think it really depends on what you want to see and experience while there. You might want to take a peek at my trip report for details of my time on Naxos so you can get an idea of whether those are things you would want to do or not. The section on Naxos begins with post # 109
With Gratitude for a Glorious Solo Month in Greece

(I haven't been to Milos and was not enamored of Santorini, and so am not a good resource about times for those islands.)

In contrast, I'm not sure that 2 full days in Athens is sufficient -- again, it depends on what you want to see and experience. For what I did in Athens, consult post # 181 +.

I've been to all those islands and think your plan is pretty good. Santorini is horribly crowded but it is so amazing that it's worth it. Three nights there, which is what you have, is good. Try to do a half day trip to one of the villages in the center of the island. You could probably take one day from Naxos and from Milos and see another island if you wanted. Another option would be to ferry from Milos to Sifnos or Serifos and ferry from there back to Athens thus cutting out one flight. I prefer ferries to flights but kids that age might get bored so your plan is fine. Those islands are small and 'easy' to do, especially if you book a hotel near the port so doing just one or two nights is OK.

Here's my report/photos (Naxos was a different trip so not included but there are photos of it) - https://andiamo.zenfolio.com/blog/20...s-milos-sifnos

Your trip is not super-short, but still, every hour is precious. That's why it's very time=wasting to go into Athens TWICE. You have to be there the night before your homebound flight anyway -- so why not go as fast as you can upon arrival to your first isle? YOu'll be tired &jet-lagged when you land, so you won't be in any condition for efficient sight-seeing in busy, bustling European capital -- nor will you have any idea what you are seeing. We "vets" know it's far better to wake up on a beautiful isle and de-lag in a slower-paced place. Then, at the end of your trip you'll be familiar with Greek ways/street signs, etc, and having been immersed for a bit in the culture, the famous Athens landmarks will resonate SO much more for you!

OK, what you need to do is research what flights (either Air Express or Aegean/Olympic) are available on arrival day (BTW, when you are asking for the best advice, it's thoughtful to give EXACT arrival date if possible, AND even time of day -- every hour affects your options.) Allow about 2 hours for getting thru passport-control lines, claiming bags, & getting a few €€ from ATMs, and checking to domestic flights. Yes, the kids will be antsy and cranky and so will you, but buy them some candy, and just push through... it's SO worth it. It also gives you at least half a day more island time.

Final note (wil be disputed by some), I'd favor shortening your Santorini time to 2 nights -- take the Blue Star 1pm ferry there, on first afternoon walk rim path, see FIRA, have sunset dinner THERE (not Oia), next AM early-early get taxi to OIA by 8 if possible, you'll have about 2 hours before the lanes become jampacked with cruise mos... then get on public bus & scram elsewhere... Maybe rent car in Fira to drive around island. For the kids, I highly recommend driving to Ancient Thira, which is a ruin atop a high high bluff (u can drive 3/4 way up).. the view is spectaular. Then Another sunset, and on AM day 3, sail away... For your kids, the Famous Caldera View will be a Yawn, and beaches are black grit, hot even to walk on. Gift them with an additional day on uncrowded isles where beaches are golden sand, and you can enjoy sunsets serenely, in tables right by the water, with no crowds... (and for you, half the price of everything).

I agree that it's better to press on the first day to an island and save all the Athens time for the end to eliminate a hotel change. However, instead of booking a separate flight, put it all on one ticket. I did this, flying to Santorini (had a layover in Rome). You will have a layover, but this way, if your initial flight is late and you miss your connection, the airline has to get you there. If your connecting flight is on a separate ticket and you miss it, you're out of luck and have to buy a new, probably expensive, ticket. After Santorini, I took the ferry to Naxos and then flew to Athens.

In response to your previous post:
In the menatime, Bluestarferries published their Rhodos - Syros timetables for June.
Monday June 8th:
Rhodos dp 7.00 - Syros ar 17.20
every Tuesday: Rhodos dp 17.00 - Syros ar Wednesday 4am
Syros - Mykonos:
Syros dp 9.10 by catamaran - Mykonos ar 9.35
Syros dp 11.30 by Bluestar ferry - Mykonos ar 12.45
Syros Island is well worth a visit.

If you do it the other way round, you can leave Syros Wednesday or Friday around 10pm, sleep in a cabin and arrive at Rhodos the following morning between 7 and 8.30 am

As to your new plans:
I wouldn't waste the (jetlagged) arrival day with transfers from the airport to Athens and back. Fly directly to Naxos or Mykonos after arrival. If you stay 1 night (or more) at Mykonos, you will have time to explore a bit. If you book the day trip from Naxos, you will not have more than 3 hrs for that.

The ferry schedule I'm seeing for Blue Star Ferries' Syros-Rhodes route only lists 2019 dates. Am I missing something or not reading it correctly? I'm looking at their website.

USe this website -- https://www.gtp.gr/RoutesForm.asp for the 2 ports put in SYR and ROD ... for the Day, leave at "any" and Month -- you will see all service for june 2020 I see M-W the ferry dep Syros late evenign, arives between 8 - 10"20 de[emdomg Fiday is faster, arrives 6:55 am.

Blue Star sails another route from Piraeus to Rhodes and back, stopping both ways en route at Santorini. That might fit better with your itinerary than the ferry from Rhodes. Either from Rhodes or Santorini it’s not a daily ferry, so you will have to plan around that. The stop at Santorini is around midnight, as it is halfway along the route.