Redirect post to category archive.

Thought something like this might work, but not sure how to make it redirect the post to it’s category archive.

<?php
/*
Template Name: Redirect To First Child
*/
if (have_posts()) {
  while (have_posts()) {
    the_post();
    $pagekids = get_pages("child_of=".$post->ID."&sort_column=menu_order");
    $firstchild = $pagekids[0];
    wp_redirect(get_permalink($firstchild->ID));
  }
}
?>

This code will get the first category and redirect to that categories page. Put this code inplace of all code on the single.php and when a post is clicked this will happen:

<?php
$category = get_the_category();
$category_id = $category[0]->cat_ID;
$relocate = get_category_link($category_id);
header("Location:".$relocate);
?>

Works great! Thanks!