Automatically insert WordPress child pages (and bbPress Forum) when publishing a page / post / custom post type (for functions.php)

wp_auto_page_children.php

<?php
//AUTO ADD WORDPRESS POST CHILDREN
function add_page_children( $post_id ) {  
	if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
	return;
	if ( !wp_is_post_revision( $post_id )
	&& 'page' == get_post_type( $post_id ) // Change as per required post type
	&& 'auto-draft' != get_post_status( $post_id ) ) {  
		$thispage = get_post( $post_id );
		$ptitle = $thispage->post_title; // Set the Parent Page title as a variable to add to new pages
		if( 0 == $thispage->post_parent ){
			$children =& get_children(
				array(
					'post_parent' => $post_id,
					'post_type' => 'page' // Change as per required post type
				)
			);
			if( empty( $children ) ){
				// 'Page Name News'
				$pagenews = array(
					'post_type' => 'page',
					'post_title' => $ptitle . ' News',
					'post_content' => '',
					'post_status' => 'publish', // Change as per post status requirements
					'post_parent' => $post_id,
					'post_author' => 1
				);
				wp_insert_post( $pagenews );
				// 'Page Name Documents'
				$pagedocs = array(
					'post_type' => 'page',
					'post_title' => $ptitle . ' Documents',
					'post_content' => '',
					'post_status' => 'publish', // Change as per post status requirements
					'post_parent' => $post_id,
					'post_author' => 1
				);
				wp_insert_post( $pagedocs );
				// 'Page Name Forum' (bbPress example)
				$pageforum = array(
					'post_type' => 'forum',
					'post_title' => $ptitle . ' Forum',
					'post_content' => '',
					'post_status' => 'publish',
					'post_author' => 1
				);
				wp_insert_post( $pageforum );
			}
		}
	}
}
add_action( 'save_post', 'add_page_children' );
?>