Hi Scoobie
Let me be the first to welcome you to HT
I can't help you with San Stefanos but can tell you a bit about Kassiopi.
Kassiopi is set around a jutting headland that forms a couple of bay areas, one is the beach and the other the main harbour. There is a nice walk that takes about 20 minutes walking round the headland past several small sandy coves that you can get to. Most of the beaches are made up of very fine shingle that lets you walk out in to the sea.
On top of the headland is an old ruined fort that you can also climb up to and get superb views of Kassiopi and across to Albania.
The main area of Kassiopi is really just 2 streets, the main street leading down to the harbour area and a street off it that leads to the other side of the headland and beach and out of Kassiopi.
These 2 streets and harbour area are where you will find most of the shops, pubs and Taverna's.
There is a good choice of eating places in Kassiopi, yes there are British style restaurants but there is an excellent choice of very good traditional Greek Taverna's also.
I can recommend in particular these Taverna's - Janis Restaurant, Petrino's & Strofilia Taverna, but there are many more for you to choose.
You won't be stuck for somewhere to eat especially if any of the children are a bit fussy.
You don't say when you are thinking of going
At the height of the season Kassiopi would be very busy and lively (NOT 18-30 style though) but this changes and the resort is much quieter out with high season and is much more couple / family orientated.
The bars may have some live acts such as bands providing entertainment some nights.
Temperatures will vary depending on when you go, with July and August obviously being the hottest, about 30 degrees, but it is never unbearable and it is cooler either side of these 2 months and starts to get a bit wetter from mid October through to May approximately.
Mosquito's can be a pest but just take a plug in killer (liquid or tablet) for each bedroom, you can buy these quite cheaply in supermarkets or chemists etc.
A repellant spray is also a good idea, the best are the kind that contain DEET, something like Jungle Formula, Autan, Boots or another chemists (Coop, Lloyds etc)) own brand.
You will find more info on Kassiopi on these link and also info on tours available, the boat in to Corfu town is a nice trip.
http://www.kassiopi-cosmic.com
I can recommend Cosmic for tours / excursions, much cheaper than tour company
http://www.kassiopi-experience.com
There is also a lot of information on Kassiopi on the link below, I will stress before you open the link that Kassiopi is not a British / lager lout resort and is still a very nice Greek resort despite some of the comments posted.
http://www.holidaytruths.co.uk/viewtopic.php?f=4&t=36108&st=0&sk=t&sd=a&hilit=kassiopi
I am sure shirley h will come on and back me up as I know she was a bit concerned before going but she loved it when she got there
Finally a few picture of Kassiopi and Corfu town -
http://travel.webshots.com/album/564110111rwhrKp?vhost=travel&start=24
Graham