Everyone’s favorite nanny alights on the Cannon Hall stage in BAM’s "Supercalifragilisticexpialidocious" 2016 summer musical, “Mary Poppins.” The Disney/Cameron Mackintosh musical tells the story of the Banks family, whose two young children have sent many a nanny packing — until Mary Poppins arrives. The show begins at 7:30 p.m. Sat. and at 2 p.m. Sun.