For my daughter's 3rd Birthday party we had a Mermaid/UnderTheSea themed Birthday Party. Thru out the year I have picked up items which made it much easier to have on hand near the actual birthday date. I bought green and blue Christmas lights on clearance after Christmas and strung them all along the doorways and dining room ceilings. I picked up a Ariel from the Little Mermaid tablecloth and cups, plates and napkins and wrapping paper..I blew up a good bunch of Green, Teal and shades of blue balloons all along the floor and hung matching  streamers on the dining room ceilings and doorways to resemble waves. I made a "Pin the Fish Tale on the Mermaid" Game and individual mermaid tales dowsed in glitter with the guests and birthday girls name on it. I played the CD that came with The Little Mermaid 2,"Limbo Rock"; Sebastian, the reggae singing crab was just great. Made my own limbo stick from a wrapping paper tube colored blue with streamers and crepe paper hanging off the ends.  I had my daughter make jellyfish from half cut paper plates painted blues and greens and she glue sticked streamers to the ends of it to resemble tentacles. She also made crabs from her two handprints centered side by side fastened with googly eyes that we hung on the ceiling. I made my own sanddollars and seahorses to hang as well. My daughter was very proud of the art work she did and she was into the spirit of her birthday even more.  I made my own piñata from a large punching ball..paper mached it and glued on seahorses painted over with shiny blue glitter.  I covered the chairs in my dining room for the girls with blue and green mesh and had them wear lei's.  I took see through cups and made blue Jell-O added colorful jellyfish and long strips of tart candy straws.  I made a sand castle cake..using funfetti cake mix..4 layers piled on top of each other frosted in the middle..then covered the entire cake frosting and baked some cake mix in ice cream cones..frosted that up too and then ground graham crackers and sprinkled over it. I took the zebra striped bubble gum and shaped flags onto lollipop sticks and wet and air dry and posted atop the ice cream cones which I centered on 4 corners of the castle. For the children's craft I took 4 baby food jars and gave the kids 5-7 pixie sticks of each color and had them pour it in as "sand art"I made a buried treasure chest out of a brown packaging box and cut out shapes of crabs ,seaweed and seahorses onto it and hid it in the yard..I made a Treasure map by printing out a map of my backyard on the computer with directions on where the kids might find their goodybags; burning it a little and pouring coffee  over it to give it the authentic look.  For the invitations I printed out time date place and glued on shapes of dolphins and seahorses on it put it into a "large" zip loc bag and had my daughter fill it with sand, tiny seashells we got here at the souvenir shop and glitter and also seatype beads enough for the girls to make a bracelet out of. It sounds like I spent a lot of money doing this but I really didn't and My only daughter turns a certain age each year only once...you bet I'll go nuts.  Next year's theme is Medieval Fairy Princess. : )~B