function _my_module_get_entityreferences_settings() {
  $child_ids = $field_names = $settings = array();

  // Get all entityreference field names
  $query = db_select('field_config', 'f');
  $query->fields('f', array('field_name'));
  $query->condition('f.type', 'entityreference');
  $query->distinct();
  $rows = $query->execute();

  foreach ($rows as $row) {
    $field_name = $row->field_name;
    $field_names[] = $field_name;
  }

  // Loop all entityreference fields. Get all child and parent Ids
  foreach ($field_names as $field_name) {
    $table = 'field_data_' . $field_name;
    $target_id = $field_name . '_target_id';

    $query = db_select($table, 'f');
    $query->fields('f', array('entity_id', $target_id, 'entity_type', 'bundle'));
    $query->distinct();
    $rows = $query->execute();

    foreach ($rows as $row) {
      $settings[$row->entity_type][$row->bundle][$field_name] = $field_name;
      $child_ids[$row->{$target_id}] = array(
        'id' => $row->{$target_id},
        'parent' => $row->entity_id,
      );
    }
  }

  return array(
    'childs' => $child_ids,
    'settings' => $settings,
  );
}

$field = field_info_field($field_name);