Get all child comments ids from parent comment id

I found this post because I was looking for a similar solution.

As suggested by Captain47, get_comments with parent args, won’t work because it’s return only 1 level nested comments.

To get unlimited nested you need to use hierarchical arg as:

           $args = array(
            'parent' => $comment_ID,
            'hierarchical' => true,
           );
        $questions = get_comments($args);

Reference: https://codex.wordpress.org/Class_Reference/WP_Comment_Query