Change ACF get_field() calls to WordPress API functions.

acf-gallery-with-acf-functions.php

<?php

function bbc_inflatable_summary() {
    $image = genesis_get_image(array('size'=>'thumbnail', 'attr'=>array('class' => 'alignnone')));
    // If genesis_get_image() does not return an image then get the first one from 'photos' field.
    if (false == $image) {
        $images = get_field('photos');
        if ($images) {
            $alt = $images[0]['alt'];
            if (empty($alt)) {
                $alt = $images[0]['title'];
            }

            $image = sprintf('<img width="%d" height="%d" src="%s" class="alignnone" alt="%s" />',
                             $images[0]['sizes']['thumbnail-width'], $images[0]['sizes']['thumbnail-height'], $images[0]['sizes']['thumbnail'], $alt);
        }
        else {
            // Use a placeholder image if the inflatable does not have any photos.
            $image = '<img width="150" height="150" src="http://www.belgrovebouncingcastles.com/wp-content/uploads/2016/07/belgrove-photo-placeholder.png" class="alignnone" alt="Photo coming soon" />';
        }
    }
    printf('<div class="one-fourth first"><a href="%s" alt="%s">%s</a></div><div class="three-fourths">', get_permalink(), esc_attr(get_the_title()), $image);
    the_excerpt();
    printf('<p>Size: %d ft x %d ft', get_field('width'), get_field('length'));
    printf('<br />Age Group: %s years</p></div>', get_field('ages_range'));
}

acf-gallery-with-wordpress-functions.php

<?php

function bbc_inflatable_summary() {
	$inflatable_info = get_post_meta( get_the_ID() );

	$images = maybe_unserialize( $inflatable_info[ 'photos' ][ 0 ] );
	if ($images) {
		$image = wp_get_attachment_image( $images[ 0 ] );
	}
	else {
		// Use a placeholder image if the inflatable does not have any photos.
		$image = '<img width="150" height="150" src="http://www.belgrovebouncingcastles.com/wp-content/uploads/2016/07/belgrove-photo-placeholder.png" class="alignnone" alt="Photo coming soon" />';
	}

    printf('<div class="one-fourth first"><a href="%s" alt="%s">%s</a></div><div class="three-fourths">', get_permalink(), get_the_title(), $image);
    the_excerpt();
    printf('<p>Size: %d ft x %d ft', $inflatable_info[ 'width' ][ 0 ], $inflatable_info[ 'length' ][ 0 ]);
    printf('<br />Age Group: %s years</p></div>', $inflatable_info[ 'ages_range' ][ 0 ]);
}