https://sridharkatakam.com/automatically-show-grid-sub-pages-static-pages-genesis/#comment-410989

page.php

<?php

add_filter( 'body_class', 'sk_body_class_pages' );
/**
 * Adds a css class to the body element
 *
 * @param  array $classes the current body classes
 * @return array $classes modified classes
 */
function sk_body_class_pages( $classes ) {

	if ( ! $post->post_parent ) { // if this is a parent Page
		$classes[] = 'sub-pages-grid';
	}

	return $classes;

}

// Display sub-Pages grid of the current Page (if it is a parent Page) after Page content
add_action( 'genesis_entry_content', 'sk_sub_pages' );
function sk_sub_pages() {

	$args = array(
		'parent' => get_the_id(), // no grandchildren
		// 'sort_column' => 'menu_order', // sort by Page Order. Remove this to sort alphabetically
	);

	$pages = get_pages( $args );

	if ( $pages ) { // if this is a Parent Page
		$pageids = array();

		// counter for adding "first" class to every third item in the loop
		$i = 0;

		echo '<div class="sub-pages">';

		foreach ( $pages as $page ) {
			setup_postdata( $page ); // to make template tag [excerpt() in this case] specific to loop

			echo '<article class="sub-page one-third';

			if ( ( $i % 3 ) == 0 ) { echo ' first">'; } else { echo '">'; }

				// get featured image URL
				$img = genesis_get_image( array(
					'post_id' => $page->ID,
					'format' => 'url',
					'size' => 'sub-pages',
				) );

				// if the Page does not have a featured image, set a default placeholder image URL
				if ( ! $img ) {
					$img = 'http://placeholdit.imgix.net/~text?txtsize=64&txt=Default%20Image&w=800&h=389';
				}

				// store the value of 'custom_page_excerpt' custom field in a variable
				$custom_page_excerpt = get_post_meta( $page->ID, 'custom_page_excerpt', true );

				// output linked image
				printf( '<a href="%s" rel="bookmark" class="sub-page-image"><img src="%s" alt="%s" itemprop="image"></a>', get_permalink( $page->ID ), $img, the_title_attribute( array( 'echo' => 0, 'post' => $page->ID ) ) );

				// linked title
				echo '<h3 class="subpage-title"><a href="' , get_permalink( $page->ID ) , '">' , get_the_title( $page->ID ) , '</a></h3>';

				// excerpt
				// echo '<div class="excerpt">' , excerpt( '20' ) , '</div>';

				echo '<div class="excerpt">';

					// if custom page excerpt has been entered for the Page, show it otherwise, the automatic excerpt
					if ( $custom_page_excerpt ) {
						echo $custom_page_excerpt;
					} else {
						echo excerpt( '20' );
					}

				echo '</div>';

				// read more
				echo '<a class="read-more button" href="' , get_permalink( $page->ID ) , '">More</a>';

			echo '</article>';

			$i++; // increment the counter
		}

		wp_reset_postdata(); // to reset setup_postdata()

		echo '</div>';
	}

	if ( function_exists( 'genesis_share_icon_output' ) ) {
		global $Genesis_Simple_Share;
		genesis_share_icon_output( 'after-entry', $Genesis_Simple_Share->icons );
	}

}

genesis();

style.css

.share-after-entry {
	clear: both;
}