Athens and side trip to one or two of the islands?

Hydra is! You can take a ferry from Piraeus (Athens port) for the day.

You can have a day trip from Athens to the Saronic Islands, Aegina, Hydra, Poros, and Spetses.

Thank you! Huge help knowing this information!

How many days do you have?

You can stay in Athens and do day trips. The closest islands would be Aegina & Agistri which will take less than 2 hours to get to depending on the type of boat.

You can do Hydra but it's a bit further but very do able for a day trip.

Avoid the three day island cruise, Aegina, Spetses, Hydra as you'll spend more time on a boat than on the islands plus it's expensive.

You can take a boat from Piraeus in the morning and spend several hours on Aegina and return late afternoon and still have time for a night out in Athens.

Aegina has everything one would want in a Greek Island and is a good introduction to the islands.

Agistri is very nice more known for it's family atmosphere and beaches.

Hydra is very popular, a bit up scale with a lovely waterfront and village cascading down to the port.

https://www.greektravel.com/greekislands/saronic.htm

Hydra is awesome. I love it so much I wouldn't want to go just for a daytrip. At least overnight. But if that's all the time you've got, Hydra is great.

Poros looks very inviting, but I've only seen it as the ferry to Hydra passes very close.

Here's an illustrated photo-album of a June day trip to Aegina, shows exactly what to expect --
http://www.flickr.com/photos/36264706@N03/sets/72157621604646139/detail/
... several important things to consider:

1) Aegina is just an hour from Pireaus -- Hydra & Poros much further
2) VERY important --either on outbound or inbound rides (if not both) to take a CONVENTIONAL ferry, that has deck seats. On a hydrofoil, no decks, assigned seats inside, salt-rimed windows, NO view. Part of ferry trip enjoyment from Pireaus is the seascape-- huge cruise ships, freighters, 3-masted schooners, fast motorboats, tiny sloops, gulls... if you're lucky, even a dolphin ... Hydra & Poros normally not served by open-deck ferries.
4) Aegina's conventional ferries are less frequent -- currently 8:30, then not til noon ... if u can't get up for the early one, take a hydrofoil, and then catch the open-deck as your return trip; leaves about 6pm (18:00).
5) If possible, go on a weekday -- Athenians flock to these islands as weekend getaway; most crowded then.

Hydra has no cars; most day-trippers just wander around the port, beaches not very available. On Aegina, you can rent a car or a scooter/atv. Or a combo of bus & taxi. You can bus to mid-island to see the awesome Temple of APhaia atop a high hiil... don't wait for another (infrequent) bus, but walk on a downhill shortcut to Ag.Marina beach, have a swim & lunch, then either bus or taxi back. OR, make a deal in port with taxi driver to take you to Temple, wait, then take you on to that beach or Marathona.

As photos show, Aegina has small but fascinating museum (man-size ancient urns), and port town has interesting back-streets, shops back there are for locals, not tourists ... gives u a glimpse of Greek towns, not so much for tourists. At seaside cafes in late afternoon, I remember being surrounded totally by Greeks, no foreigners.

Aegina is just an hour from Pireaus -- Hydra & Poros much further

Hydra is just 90 minutes from Piraeus. Poros just 75. So not that much further.

Hydra has no cars;

That's exactly why we love it there.

As you see, different people enjoy different things. I've never been to Aegina, but our time in Hydra is something we'll keep with us for the rest of our lives.

AEgina is 1 hour if you take the open-deck ferry... the closed hydrofoil, as used for Hydra, takes just 40 minutes.

Thank you so much everyone for all the great information. We would probably be in Greece for 7 days (Spring Break) I like the idea of "family friendly" environment. I have heard stories of beach situations in Greece that left some people feeling uncomfortable with their families and kids present (love on display in public if you know what I mean).

All of these islands are "family-friendly" and are popular with Greek families as well as tourists. I have been to beaches on more than 25 Greek islands ... all of them beaches that are NOT known as clothing-free (nudist) beaches, and have never seen anything that might startle a child. I am not quite clear about what is "uncomfortable" for your children? When u say "you know what I mean" I am guessing you mean actual sex acts. If you are referring to people embracing or kissing I am not sure that beaches anywhere in the world would be safely affection-free, unless one limits oneself to beaches controlled by restrictive religious sects.

As for dress habits, in beaches all over Europe, sunbathing women have been known to slip off their tops from time to time. And at one of my favorite beaches on Naxos, shallow and safe for kiddies, toddlers sometimes waddle alonog the waterline in their birthday suits. No one seems to mind.