Start with a piece of cardboard from a cardboard box.
Cover it in blue paper, then cut out some sand colored paper for the beach part at the bottom.
Glue colored sand to the beach to give it the texture of sand.
Print various sea animals to stick on the scene. Laminate the animals, put double sided tape on the back of them. Stick them to some cloth first to make it less sticky (you want to be able to remove them).
