Using hook_menu to add a child to a menu item
An example child item would just fall under the parent item in the path hierarchy, no need for plid.

e.g

  $items['admin/sponsorship/child'] = array(
    'title' =&gt; 'Sponsor child',
    'description' =&gt; 'This is where all of the child sponsorship data is stored',
    'page callback' =&gt; 'mymodule_sponsor_child_page',
    'access arguments' =&gt; array('access sponsorship section'),
    'type' =&gt; MENU_NORMAL_ITEM
  );


system_menu has some good examples of menu item containers, using system_admin_menu_block_page,  e.g admin/appearance/*

Make sure you clear menu cache to get any new menu item to show up there.