Make scuba masks for your guests to wear. Cut 1-inch wide, oval-shaped borders out of poster board or other heavy paper. To make the lens, tape clear cellophane behind them. Attach a piece of elastic to each side of the masks so they can be worn. Create a treasure chest out of a large shoebox. Cover the box with brown construction paper and pieces of gold foil or glitter paint. Fill it with shells, craft jewels, plastic necklaces and plastic gold coins.
Wrap Styrofoam rings with red ribbon to make life preservers. Hang them around the party room, or hang them from the back of each chair. Use plastic blue table cloths to cover the tables, and decorate it with clean sand, sea shells, beach glass and plastic jewels. Use any ocean-life toys as table toppers or centerpieces. Cut out fish and other ocean life shapes from construction paper or poster board, and decorate the party space with them.
Make sea water by mixing apple juice with blue food coloring. For an extra touch, add plastic aquarium plants to the pitcher. Make shell biscuits. Take homemade or store bought biscuit dough, and make an indent in the bottom of the circle with your thumb. Then, make a few shallow cuts along the top to create a scalloped look. After the biscuits have been baked, add a little bit of your childs favorite jelly or jam to the indented part of the biscuit. Make ice cream octopuses. Put eight licorice whips on each plate, and top with two scoops of ice cream, one larger then the other. Use icing or candy to give them each a face. Using cookie cutters, make fish shaped sugar cookies.