I am looking for a book my Grandmother had when I was a child. It was a children’s chapter book published in the 80s or early 90s, and was likely something she got either through a book club or at a yard sale. It seemed like it was intended to be part of a series, though I don’t know if any other volumes were ever published. The book was about a pair of siblings (I believe it was a brother and sister, though it could have been two sisters), who were attending summer camp. They were either not getting along with each other, or not enjoying camp and were unhappy. In the middle of the night, another brother and sister appear and invite them to come with them to a magic carnival. They ride a canoe up a moonbeam to the carnival in the sky somewhere. There they see all sorts of incredible characters and shows. There is an octopus running a game booth. And at the end there is a dolphin race where the children ride the dolphins and one of the siblings wins (their earlier angst may have been a result of one of them losing a race at camp??). Over the course of their adventures, the siblings mend their differences and at the end are returned to camp ready to enjoy the rest of their summer. Something about the book, either a summary in the back or something on the back cover, implied that there would be other books where different kids who were having problems would be taken to the carnival to sort them out. I have been searching for info on this book for years and any help would be much appreciated!