We did Vero Beach in 2001 for a weekend through DVC.
It is a lovely resort with a nice beach area, wonderful views of the ocean from our room, great pool area with slide. There are things you can rent at the beach including a hobicat and jet skis. There is 9 hole mini golf and depending on what time of the year you go, there is a thing where you go and see the turtles come up and lay their eggs.
They have a campfire sing a long every night which is fun for the kids; they do smores and sing songs. Watch out for the noseeums; they are vicious little bugs. My legs were covered with bites. I hear that Skin So Soft repells them (unfortunately, I found out too late).
We did not do any special activities other than the campfire because the kids had never done a beach, and we spent a long time on the beach.
Check over on the DVC board; you will get lots of answers there since it is a DVC property.