you need to use a custom query to pull the galleries that you need including the child albums, use the taxonomy option, add it before the look, something like this

$args = array(
'post_type' => 'ims_gallery',
'tax_query' => array(
array(
'taxonomy' => 'ims_album',
'field' => 'id',
'terms' => array("IDS")
)
)
);
$query = new WP_Query( $args );