Flea Island is a small, uninhabited island. To get there from the beach, one must take a small rowboat.
In Escape From Flea Island, Martha, Carolina, Helen Lorraine, Alice Boxwood, Truman Oatley, Tiffany Blatsky, and T.D. thought they were shipwrecked there for Carolina's science project, but in reality, they were just at a far-flung corner of the beach and the ship wasn't even wrecked.
In Skits and Mr Scruffles, the Lorraine family go to the real Flea Island on a picnic because they think Skits is lonely or bored when he speaks of Milo, who at that stage, they thought was imaginary.