Sky Island (version 2) by L. Frank Baum (1856 - 1919)

A little girl (Trot) and her friend (Cap'n Bill) team up with a young boy named Button-Bright. Button-Bright had found a magical umbrella in his attic. He meets the kind girl and sailor and they are transported to a different world in the sky where he and his friends face many dangers. (Summary by francesb)