joomla: fetch last 4 articles from current category subcategories

klumba_category_slider.php

/*
 * get subcategory ids
 */
$catID = $this->category->id;
$categories = JCategories::getInstance('Content');
$cat = $categories->get($catID);
$children = $cat->getChildren();

$children = array_map(function($el) {
    return (array)$el;
}, $cat->getChildren());

$ids = array_column($children, 'id');
if (is_array($ids)) {
    $ids = array_merge(array($this->category->id), $ids);
} else {
    $ids = array($this->category_id);
}

/*
 * get articles
 */
$db = JFactory::getDbo();
$query = $db->getQuery(true);

$query->select('*')
    ->from($db->quoteName('#__content'))
    ->where($db->quoteName('catid') . ' in (' . implode(',',$ids) . ')')
    ->order('created DESC');

$db->setQuery($query, 0, 4);
$articles = $db->loadObjectList();