A Story about Sea Animals; But really about us

Laura and David are just like every other sister and brother. One beautiful, sunny day while on their way home from school they discover an under-water world that's just outside their backyard. Well, they don't just discover this world, they fall INTO it. They are befriended by a big blue whale who turns out to be their tour guide on a journey into a secret world where normal sea creatures aren't normal after all.