protected function getChildrenList()
    {
        return (new Query())->from($this->itemChildTable)
            ->all($this->db)
            ->then(
                function($rows) {
                    $parents = [];
                    foreach ($rows as $row) {
                        $parents[$row['parent']][] = $row['child'];
                    }

                    return $parents;
                }
            );
    }