It doesn't have a meaning. It's a Mickey Mouse Club chant ("Meeska Mooska Mickey Mouse!") used to summon the Clubhouse.
Anecdotal sources suggest that these words are supposed to be words for "mouse" in different languages. In Serbian a word for mouse, is "mish" and a diminutive is "mishko". In Russian, if you add a diminutive suffix to the word “mysh” (mouse) it turns into “myshka” which means "little mouse.
Mickey Mouse Clubhouse focuses on interacting with the viewer to stimulate problem solving. Each episode has the characters help children "solve a specific age-appropriate problem utilizing basic skills, such as identifying shapes and counting through ten."
Watch full length TV episodes, video, clips and music videos from the Disney Junior series Mickey Mouse Clubhouse at Disneyjunior.disney.com.