Lounge chairs and beach blankets, and beach balls instead of balloons. Holding the party outside? If you have a sandbox, place fake crabs and other beach sea creatures in the sand. Have a wading pool so the kids can cool off. If you're holding the party indoors, cover the walls in blue ocean coloured paper where children can draw fish.
Make Mexican beach type foods like nachos, quesadillas, etc. Have fruit smoothies to drink.
Rice Krispies* Treat:
Prepare the original Rice Krispies recipe, pressing the mixture into a cookie sheet. Once set, use a fish shaped cookie cutter to cut out little fishes. Let the kids decorate their own fish with supplies like icing, candy eyes, sprinkles and any other tasty additions.
SAND CASTLE BUILDING CONTEST
Have lots of prizes for things like the tallest, the smallest, etc.
PIN THE FLIPPER ON THE DOLPHIN
Just like Pin the Tail on the Donkey. Draw a dolphin on poster board, and mark where the flipper should go. Cut out a flipper for each kid and put some double sided tape on the back. Let each child have a turn a pinning the flipper on the dolphin (blindfolded and spun around three times).
Buckets with shovels fill the buckets with sunglasses, bubbles and a beach ball or other things which may help the kids with the sand caste building contest.
Invite the kids to come dressed in beach attire, like Hawaiian shirts for boys, and grass skirts for girls.