Have the child create her own plastic bag aquarium. Take a gallon-size plastic bag that seals at the top and use this as your aquarium base. Cut a sheet of blue paper that fits inside the sealed bag and give this to your preschooler. Have the child decorate the blue paper like an underwater scene. Place the completed background in the bag and fill the bottom of the bag with coffee grounds to mimic the sea floor. Seal the bag well and display the aquariums around the classroom.
Blow up a balloon and use this as the base for the octopus's body and head. Allow the child to decorate the face and body of the octopus with eyes and a mouth. He can either draw directly on the balloon using an appropriate marker or provide him with stickers that represent the animal's facial features. Cut strips of crepe paper and attach them to the balloon to represent the octopus' eight legs. This craft can also be incorporated with a math lesson about counting and the number eight.
Provide the child with an undecorated drawn fish. You can draw a fish using a marker and white construction paper or print out a black and white outline from a computer. Allow her to decorate the fish any way she chooses. Provide her with markers, glitter, or any other craft materials you have around the classroom or home. Ask the child to create a story about the fish she created and tell this to you or the class.
After teaching the child about the variety of animals that exist under the sea, create puppets based on these animals. Provide him with small, plain cutouts of sea animals such as fish, sea urchins, sharks and dolphins. Use a heavyweight paper as the base for the animals to provide stability to the cutouts. Allow the child to decorate the animals using any available art materials. Glue wooden sticks or straws to the back of each sea creature to allow the child to hold the puppet. Ask the child to put on a puppet show for you or the class using their under the sea animals.