The best place for little kids at SAB is on the Yacht Club side. There is a shallow, sand bottom area that's great for building castles, etc. Also, there is a smaller slide at the base of the pirate ship. You have to go onto the beach to get there. Nice also.
I also recommend the gelato at the Marketplace. And walk over to the boardwalk at night and watch the street entertainment. And the fireworks.
Jenny