foreach ($children as $cat) {
$querystr = "
SELECT DISTINCT $wpdb->posts.ID
FROM $wpdb->term_taxonomy, $wpdb->posts, $wpdb->term_relationships
WHERE $wpdb->posts.ID = $wpdb->term_relationships.object_id
AND $wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id
AND $wpdb->term_taxonomy.term_id = $cat->term_id
AND $wpdb->posts.post_status = 'publish'
AND $wpdb->posts.post_type = 'post'
AND $wpdb->posts.post_date < NOW()
";
$querystr = $wpdb->prepare($querystr,'');
$result = $wpdb->get_results($querystr, ARRAY_A);

if ($result)
foreach ($result as $id)
$subcatposts[] = $id["ID"];
}