At my son's splash party for his preschool class, we had a Hawaiian theme.  The garage was decorated with cut outs of palm trees, pineapples, large tissue paper flowers, and topical colored streamers. The kids were given lais and I even wore a grass skirt.  We had a pool and lots of games.  The kids had a water balloon toss, a pie eating contest(cool-whip in a CLEAN metal ashtray)-they really enjoyed this one, pin the tail on the fish, egg in a spoon race.  The winners got ribbons instead of prizes.  The kids also played musical chairs, did the limbo, the chicken dance, and had a fish pond for a prize.  We  had a tropical rain forest tape playing in the back ground.  We had cupcakes, chips in a large sea shell bowl, dips, chicken tenders, and popcicles.  The invitations were wild bright tropical fish done on the computer and t-shirts were done to match.