Songs with ocean themes are a good way to introduce preschoolers to the sea. Some favorites include "My Bonnie Lies Over the Ocean" and the "Fishy Pokey," sung to the tune of the "Hokey Pokey" ("Put your left fin in, take your left fin out," etc.) Another song is "I'm a Little Fishy," sung to the tune of "I'm a Little Teapot." ("I'm a little fishy, watch me swim. Here is my tail, here is my fin. When I want to have fun with my friends, I wiggle my tail and dive right in.")
Take a clear plastic soda or water bottle and fill it two-thirds full with water that you've tinted blue or green with food coloring. Add a small amount of baby or vegetable oil, some gold glitter (to resemble sand), a few small shells, and aquarium gravel. Replace the cap on the bottle, and seal it with tape so it wont leak. When you tip the bottle to its side, the moving water will resemble waves.
Have students stand in a large area where they have room to move around. Tell them you're going to call out the names of animals and fish. When something you say lives in the water, they should move their arms as if they're swimming. If its a land creature, they should walk in place. You have almost endless options, including sharks, whales, tigers, dolphins, monkeys, starfish, seahorses, cows, pigs, chickens, seals, otters, raccoons, etc. Play as long as the children show an interest.
Give each student an aluminium pie tin and small cup of water. Ask students to pour the water into the pie tin, to represent the ocean. Explain that wind blowing on the ocean creates waves, so have students blow gently on the water to make their own waves. Explain that waves will be large or small, depending on the force of the wind. This experiment can also be performed in front of the class using a shallow casserole dish and a small fan.