Sigmund and the Sea Monsters (2016)

Johnny and Scotty are two brothers spending the summer in the seaside resort town of Dead Man's Cove, helping their aunt Maxine and cousin Robyn run their cafe. One day, while collecting trash on the beach, they discover a friendly, young sea monster named Sigmund. The boys and Robyn become friends with Sigmund and teach him about the human world. The kids have to keep Sigmund a secret from everyone especially Captain Barnabus who is determined to capture a sea monster and prove their existence.