We had a backyard "splash party" for my daughter's 7th birthday. We made the invitations with tropical fish and dolphin stickers, and told the kids to wear their swimsuits.  In our backyard, we set up a big inflatable pool, sprinkler, and slip-n-slide for them to splash in. When they arrived, we laid out their towels in the backyard and handed out leis, sunglasses and sunscreen. They played in the water (the slip-n-slide was a big hit) and posed for lots of pictures together. Then we served lunch that included tropical fruit, sandwiches, blue fish Jell-O (finger Jell-O cut out with fish cookie cutters) and goldfish crackers. To drink, they had blue kool aid served in clear plastic cup with tiny fish stickers so their cups looked like aquariums.   The birthday cake was decorated like the ocean with a dolphin on it.  After cake they decorated fish shaped cookies to bring home.  My daughter opened presents with Beach Boys music playing in the background. The girls had a blast!