Looking for a nice family place in Thailand (October)

My wife and I want to take the kids to Thailand later this year. We need to be there anyway, since an American friend of ours is getting married in Bangkok mid October.

We are wondering on advice for a nice resort to stay at for about three nights. We will be with the two of us and our six year old boy twins.

We look for authenticity, safety, friendlyness and swimming for the children. We are currently thinking of Koh Samui.

BTW, we are Europeans, so we might be a bit more adventurous than the average American. Cultural chauvinism shows ;-)