Support external images in the XML sitemap if using All in One SEO Pack on your child site.
Snippet Type
Execute on Child Sites
Snippet
add_filter( 'aioseop_images_allowed_from_hosts', 'my_aioseop_images_allowed_from_hosts' );
function my_aioseop_images_allowed_from_hosts( $hosts ) {
$hosts[] = '*.wp.com';
return $hosts;
}