What Is the Name of This Book? question

Ok so there's a book I read when I was younger, and I was hoping to read it to my little sister. The only problem is that I can't remember the title!! It's about three siblings who go to an island every summer to visit family and the daughter finds a bottle in the ocean with a message in it. It is a four book series, each book titled after an element. In each book the siblings go on adventures based on that element. For example, for Air they had to make wings and fly and for Fire they had to step through fire. If this sounds familiar please help!! :)