October is beautiful on the Island. Swimming should still be okay in the Ocean. Of course it won't be as warm as August. In August, as you know, is like bath water.
As far as new resturants, Marley's is fairly new. We like it. Sometimes it gets loud, but it's a fun atmosphere.
Have a great time on Hilton Head.
Don't forget to visit South Beach, they have lots of activities for children by the salty dog and during this summer they are starting Hermit Crab races by the shops. If you go on the Gypsy, dolphin trip, they send all the children over to a shop to get a FREE shark tooth. It's small, but the children love it because it came from a real shark.