The Folk of the Faraway Tree By Enid Blyton

Jo, Bessie and Frannie are fed up when Connie comes to stay - she's so stuck-up and bossy. But they don't let her stop them having fun with their tree-friends, Silky, Moon-Face and the Saucepan Man. Together they climb through the cloud at the top of the Faraway Tree and visit the wonderful places there, the Land of Secrets and the Land of Treats - and Connie learns to behave herself