Add Post Format Support to Twentyeleven Child Theme

try running your code with a lower priority:

add_action( 'after_setup_theme', 'my_twentyeleven_setup', 20 );

function my_twentyeleven_setup(){
  add_theme_support('post-formats',  array( 
     'aside', 
     'chat', 
     'gallery', 
     'image', 
     'link', 
     'quote', 
     'status', 
     'video', 
     'audio',
  ));  
}