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' => 'Sponsor child',
    'description' => 'This is where all of the child sponsorship data is stored',
    'page callback' => 'mymodule_sponsor_child_page',
    'access arguments' => array('access sponsorship section'),
    'type' => MENU_NORMAL_ITEM
  );

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

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

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' => 'Sponsor child',
    'description' => 'This is where all of the child sponsorship data is stored',
    'page callback' => 'mymodule_sponsor_child_page',
    'access arguments' => array('access sponsorship section'),
    'type' => 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.