<?php

// Include Wordpress framework/API
require_once( '/path/to/wp-load.php' );


// Get parents (level one)
$items_level_one = $wpdb->get_results(
	'SELECT
		*
	FROM
		wp_posts
	WHERE
		post_type = "Page" AND
		post_status = "Publish" AND
		post_parent = "[put parent id here]"
	ORDER BY
		menu_order,
		post_title',
	ARRAY_A
);

print_r($items_level_one);

?>

<?php

// Include Wordpress framework/API
require_once( '/path/to/wp-load.php' );


// Get parents (level one)
$items_level_one = $wpdb->get_results(
	'SELECT
		*
	FROM
		wp_posts
	WHERE
		post_type = "Page" AND
		post_status = "Publish" AND
		post_parent = "[put parent id here]"
	ORDER BY
		menu_order,
		post_title',
	ARRAY_A
);

print_r($items_level_one);

?>

Plugin gets child pages of parent in Wordpress. You'll need to pass the parent ID but this isn't difficult to figure out programmatically if needed, either.

Get children of parent with MySQL SELECT query

mysql, wordpress

PHP