When you use WordPress as your CMS, there are many things you can do. Often you can do things with a plugin designed for the task. In the case of showing a page list with thumbnails, this can be done with a simple and free WordPress Plugin.
<h2>Using the Page-list Plugin for WordPress</h2>
<img class="alignnone size-full wp-image-7394" src="https://itxdesign.com/wp-content/uploads/2014/11/PageListPlugin.png" alt="PageList Plugin" width="565" height="263" />

Start by downloading the <a href="https://wordpress.org/plugins/page-list/">Page-list Plugin for WordPress</a>. This plugin will allow you to do exactly what you need to do as soon as it's installed.

Once installed, you won't need to actually access the plugin to use it. Instead, you will use the shortcode [pagelist] to display a list of your pages. This shortcode can be inserted into a new page and will display the list of pages for your website in a list.

<img class="alignnone size-full wp-image-7393" src="https://itxdesign.com/wp-content/uploads/2014/11/PageList.png" alt="PageList" width="318" height="228" />

This simple nested list can be used anywhere on a page, post or even in the text widget. However, if you have a site set not to allow shortcodes in your widgets, you may need to change the setting within your functions.php file.
<h2>How to Display Child Pages</h2>
The [subpages] shortcode will work with this plugin and allow you to show child pages on a parent page. This is one of the easiest ways to display child pages. You can also use this shortcode to display the child pages within a text widget.
<h2>How to Show Sibling Pages</h2>
You can also show sibling pages with this plugin by using the shortcode [siblings]. This shortcode can be used on a page, post or within a text widget, as well.
<h2>How to Show your Page List with Thumbnails</h2>
If you want to show your page list with a thumbnail, you will need to use a different shortcode. The shortcode for this is [page_ext]. You can use this shortcode to show a thumbnail image and you can actually adjust the size of the image, as well. The shortcode would look like this:

[pagelist_ext show_image="3" image_width="50"]

This code will show image "3" and will give it a width of "50".

Along with using a thumbnail, you can show an excerpt and control the length. This is done with the same shortcode and by adding the limit_content tag. You can also turn the content off with the show_content tag with a setting of "0".

These are just some of the things you can do with the Page-list plugin for WordPress. There is a full list of parameters you can within your shortcodes found <a href="https://wordpress.org/plugins/page-list/">here</a>.

If you want to display page lists on your WordPress website and be able to control how they look, this is one of the best plugins for it. You can show many different types of page lists in so many ways with the plugin.