D.H.
Hi M. ~
I know you've been to Key West, but that is deffinitely the first place I thought of. Yes, there's alot of partying, but mostly at night...there's alot of water stuff to do during the day..dolphin watches, snorkeling, the beach...
Also, what about Clearwater Beach? It's on the Gulf Coast...that side is so much nicer than the ocean side! The sand is soft, white and the water blue...and wonderful sunsets.
We've stayed in Ormund Beach, too, which is about 5 minutes north of Daytona...beach was OK, not as much for kids...but still have alot of water activities...and about 45 minutes from Kennedy Space Center (although your girls are probably a little young for that yet).
have fun!
D.