designtopack/public/site/models/project.php

<?php

class ProjectPage extends Page {
  public function getSteps() {    

    $steps = array_map(function($child) {
      return [
        'text' => $child['content']['title'],
        'value' => $child['content']['stepname'],
        'index' => $child['content']['stepindex']
      ];
    }, $this->children()->toArray());

    usort($steps, function ($a, $b) {
      return $a['index'] <=> $b['index'];
    });

    return $steps;
  }
}