Decorations

From brown paper or cardboard, cut out the shape of the underneath of a boat and hang it on the ceiling. Hang a cardboard anchor tied to a rope from the boat. Also, hang a fishing pole from the boat's side with a fishing line and a plastic worm dangling from it.

Hang teal, royal blue, sea-green and light blue crepe paper streamers of varying lengths from the ceiling to create the effect of being under the sea (glue cut-out fish to the ends and middles of these strips). You could get some orange and red helium filled balloons like sea bouys, to tie the crepe paper to if you don't want to risk damaging your ceiling! You can also hang fishnets and on them hang fish cutouts and various sea-life creatures.

Hang cardboard fish and seahorses from a clear fishing line to appear as if they're swimming around, and sprinkle various stuffed sea-life creatures around the house. Make jellyfish from half-cut paper plates with streamers attached to resemble tentacles.

Get a few rolls of brown paper and place it on the floor to give the appearance of a sandy ocean floor. Also, place lots of blue-shaded balloons on the floor to create an ocean effect.

On the tables, put a blue tablecloth with green strips across and hanging down from the edges (for seaweed). You can add fish to the end of each strip. Seashells can be used as table confetti. You can also cover the tablecloth with fish net.

If you have fluorescent lights, take blue and green crepe paper and cover the exterior of the lights so it gives the room a watery appearance. You can also buy some blue and green light bulbs to put around the house to really give the under-the-sea kind of feeling. Another good way to achieve this effect (if you are having your child birthday party during the day) is to buy blue and green cellophane paper and cover all the windows in the house and enjoy the blue-greenish light immerse the house.  For extra effect play an Ocean Sounds CD.