HI folks, hope this looks better.
Using javascript works for me. Include following code in template file:
<?php
//If portfolio page make first child the current page
$portfoliopage = $pages->get(1019);
$posts = $pages->find("parent=$portfoliopage, sort=title");
if($page == $portfoliopage):
$url = $posts->first()->url;
?>
<script type="text/jscript">
location.replace("<?= $url ?>");
</script>
<?php
endif;
?>
You can sort the posts array any way you like. For the latest addition use "sort=-sort"
Success!