Add children to Post Object

function.php

<?php

function add_children_to_pages($response) {
  
  foreach($response['posts'] as $index => $post) {
     
    $args = array(
      'post_type'       => 'app_pages',
      'posts_per_page'  => -1,
      'post_parent'     => $post->ID,
      'orderby'         => 'title',
      'order'           => 'ASC'
    );

    $child_pages = new WP_Query( $args );
    
    $post->children = array();
    
    foreach($child_pages as $i => $child) {
      $post->children[] = $child;
    }
  }
  return $response;
} 

add_filter('appuccino_get_pages_response', 'add_children_to_pages', 10);
?>

template.html

<p ng-bind="post.post_title"></p>
<ul>
  <li ng-repeat="child in post.children" ng-bind="child.post_title></li>
<ul>