get_pages problem with home page

function site_child($pid) {
 
	$site_term = io_multi_get_var('term', null);  //this is coming from a different function. it works.
	$args = array(
		'child_of' => $pid,
		'hierarchical' => 0,
	);
	// http://codex.wordpress.org/Function_Reference/get_pages
	$children = get_pages($args);
 
	foreach ($children as $child) {
 
		if ( has_term($site_term,'site_assign',$child) ) {
			//echo $child->ID;
			return $child->ID;
		}
	}
	return false;
}
 
// modify the PAGE main query
function replace_content_with_child( $query ) {
	global $wp_query;
 
	if( $query->is_main_query() && !is_admin() && is_page() ) {
		$id = get_queried_object_id();
 
		if( $sitechild = site_child($id) ) {
 
			$query->query_vars['page_id'] = $sitechild;
		}
	}
}
add_action( 'pre_get_posts', 'replace_content_with_child' );