function getParents($childPostId, $parentPostType, $acfKey) {
    return get_posts(array(
        'post_type' => $parentPostType,
        'meta_query' => array(
            array(
                'key' => $acfKey,
                'value' => '"' . $childPostId . '"',
                'compare' => 'LIKE'
            )
        ) 
    ));
}