There are so many SpongeBob invitations available out there for all kinds of celebrations. But if you don't find one that you like for your SpongeBob baby shower, simply make your own by looking for a great picture on the internet and using it as a background for your invitation or as a cover picture. You could also accent the invitation by using dimensional and glitter pens to highlight the seaweed or bubbles in the picture.
Obviously, SpongeBob is a really watery theme so the color scheme would be blue and green plus SpongeBob's yellow and red for accents. Aside from using the commercially available SpongeBob decorations, you could also use plain blue, green, yellow, and red balloons, streamers and tableware to extend the color scheme. Rent a bubble machine, if you can, since SpongeBob loves bubbles.
Use plain colored tablecloths in the chosen color scheme. You can alternate colors for a really fun effect. For the centerpiece on the tables, you could alternate with SpongeBob figures and real or fake pineapples. Set each one in a glass plate and surround it with white sand and beach-related items like shells, starfish, marine colored glass pebbles, and maybe a few aquarium toys like treasure chests or fake fish.
The buffet table can be highlighted by a large SpongeBob character in the middle of a flower arrangement of red and yellow daisies or gerberas. A large Mylar SpongeBob balloon can be attached to one corner of the buffet table to stand guard over the food. Use a watery-patterned fabric to cover the buffet table and preferably have clear glass platters to serve the food. Have some plastic fish “swimming” among the platters to add to the underwater feel.
SpongeBob is famous for his “Krabby Patties” and there's no reason for you not to serve crab cakes at this SpongeBob baby shower. Search for one of those delicious crab cake sandwich recipes on the internet and try it out. Have some really good mayonnaise, mustard, mango or green tomato chutney, lettuce, tomato slices, and cucumber slices on hand for a make-your-own crab cake sandwich extravaganza. Use really good crusty bread rolls for this, nothing else will do.
Supplement the crab cake sandwiches with a light green salad with a fruity dressing and you're done. For dessert, Pineapple Upside-Down Cake is a great choice, as is a Hawaiian Wedding Cake. A wonderful dessert to serve on the side would be square cookies with SpongeBob's face iced onto them.
Favors for this fun party could include a bubble blower and a candle
or soap in the shape of SpongeBob. Finish off the loot bag with
dried pineapples and other dried tropical fruits, and pack it all
into a beach pail set.