Children links disappear when access to parent blocked
With the caveat you should be very careful adjusting any core menu item permissions, and I'm presuming you know what you're doing there, it is possible to adjust any menu with

hook_menu_alter

for example:

function mymodule_menu_alter(&amp;$items) {
  // Enable open access for everyone to foo/bar
  $items['foo/bar']['access callback'] = TRUE;
}


You can also specify your own access callback there, e.g

function mymodule_menu_alter(&amp;$items) {
  // Add custom access callback to foo/bar
  $items['foo/bar']['access callback'] = 'mymodule_special_access';
}

function mymodule_special_access(){
  global $user;
  if($some_condition_is_true){
    return TRUE;
  }
  return FALSE; // default deny
}