We threw an "Under The Sea" party for my daughter's sixth birthday.  The invitations had a clip art mermaid saying "come with me to a party under the sea."  My daughter greeted everyone at the front door in her mermaid Halloween costume. We filled our front room with different shades of blue and green helium balloons. There were at least 200 of them, all with blue or white strings hanging down to give the feeling of being underwater. We had blue and white streamers everywhere to represent waves and air-filled balloons for the kids to kick around.  We also had inflatable fish all around the place including a six foot shark hung from the ceiling.  My daughter and I worked for weeks coloring and painting ocean themed pictures (including Ariel, Sponge Bob, The Rainbow Fish, and other popular characters) to decorate the walls. We set up our collection of playhuts and covered them with blue blankets to create an underwater cave maze. We decorated our guest room like the front room, covered all the furniture with blue blankets and towels, and covered the floor with a brown tarp.  We then set up an automatic bubble blower and set out tubs of bubbles and lots of bubble wands.  Kids were running in and out of the bubble room the entire party.     In preparation for the party, I covered empty tissue boxes with blue wapping paper leaving the opening at the top. I then painted them with blue glitter glue.  At the party the kids played an octopus ring toss game to win foam fish to glue onto them to make aquariums.(We let the kids come back and win extra fish as often as they wanted). These then became their party favor and prize boxes.     We had an inflatable Sponge Bob that kids threw crabby patties at to win fish themed bubbles, and a pin the flower on the mermaid game where everyone won a fish pencil and notebook. The big winners of the games got to keep one of our stuffed fish or lobster decorations(bought at the dollar store). For a craft they decorated their own treasure necklace with fish and shell shaped beads. (The necklaces were film cannisters hung on a string and covered with a  "treasure" label.)  Everyone also got to pick out a Perler Bead zipper pull that my daughter and I worked on for months before the party.  The zipper pulls were all different (sea horses, mermaids, crabs, and fish) and were the talk of the school for a long time after the party.     For food we had goldfish, homemade gummy sea creatures, and blue jello with gummy fish inside. My husband made a beautiful ocean scene cake.  The bottom layer had sand colored icing with iced on sea creatures. The top layer was blue and up on wedding cake pillars. He used spun sugar to make a waterfall from the top layer to cover the bottom layer.  We also had cupcakes with blue icing and hand drawn fish.   We ended the party with two homemade fish pinatas filled with candy and stickers.  We needed two because we had almost thirty kids at the party and we wanted everyone to have a chance with the bat.      The thank you notes had the same clip art mermaid on the outside as the invitations. On the inside we typed a personal thank you on one side and had a clip art sea themed frame on the other.  I cut out the center of each frame and taped in a picture of my daughter with each guest and the gift that they brought. If there was no gift we typed out a thank you for celebrating with us and included a picture of the guest at the party.