Kamari is probably your best bet for things to do for families, followed by Perissa.
For beaches remember they are mostly coarse black sand which gets VERY HOT!!! although the sea is lovely and shelves away quite nicely!

Personally I don't think Santorini is geared up for families. It's more couples. I agree that Kamari is the best place if you are going to go as there are plenty of restaurants and a fair few shops. Try Nostalga on the right hand end of the front if you were standing on the beach and looking inland. Their mixed grill is superb. The restaurant above the tour booking office is good and quite swish for greece. You get your wine in a proper glass caraff rather than a beaten up tin jog, and when we went their was a chap playing the piano - tasteful stuff, not rolll our the barrel! There is an italian place, which I think is more on the left hand side, that is just to die for. The chef makes the pasta on a table on the front of the restaurant so you can see him make the tagliatelle, etc that you are going to eat. The beach at Kamari is black shingly pebbles whilst the beach at Perissa is coarse sand. My idea of heaven is to sit in one of the restaurants in the capital town of Thira, have a fantastic greek meal and watch the sun go down over Thirissa, which is the island across the Caldera (sea). You can get to Thira by bus for next to nothing and they run until about 1am, but don't leave it while the last minute cos they do pack 'em in and if you don't get a seat you end up getting up close a personal with complete strangers! We went to Skiathos last year and if beaches are your thing this is the island for you. The bus starts at Skiathos Town and goes along the bottom of the island to Koukanaries, stopping at about 15 beaches on the way. You can get off where you want but again they pack 'em on and if you are wanting to go back to your apartment you have to pick your time as you may have to wait a bit as the first few buses may be full and will sail past you. There's plenty to do in Skiathos Town for adults and kids and I would recommend that you stop in Town and bus it out to the beaches. Never been to Kefalonia but it's the favourite island on 2 of my friends and from what I have been told I think it's for couples again. Hope this helps! Santorini is my favourite and I would suggest that you what until the kids are old enough to be wanting to go to Falaraki will their mates and you and your partner take off to Santorini by yourselves!

ANNETTE - So dp you think Skiathos Town is geared up for families ?
I wasnt sure if it may be a bit noisy/rowdy late on an evening

hi I'm sending this post from Kamari Santorini. In my opinion life here is based mainly on restaurants. There are no pubs as such, hence no pool tables, quiz machines etc. The people welcome small children but we have been here 10 days and not seen anything for them to do specifically, - no parks etc. The beach is boiling hot and the sea shelves steeply. If you bring children here I'd suggest you choose accommodation that provides family entertainment. Santorini is a beautiful island ( we've been around it all on quad bikes) but in my opinion it is mostly suited to couples.