Fill the balloon with water . This image illustrates why you don't completely fill the balloon you should always leave some room in the neck of the balloon, then as the form dries the pressure has somewhere to go and your clay wont split like that.
Each student created 2 or 3 paper and oil pastel tridimensional pieces based on a template a created. After each pieces was assembled, I put them together in a Racimo (a banana bunch!), a hanging art piece.