Function for create a shortcode to display subpages

Wordpress: Shortcode list child pages

	<?php function childpages_shortcode( $atts ) {
	
	    global $post;

	    $args = array(
		'post_parent' => $post->ID,
	        'post_type' => 'page',
	        'depth' => 1,
            	'orderby' => 'menu_order',
            	'order' => 'ASC'
	    );

	    $childpages .= '<ul>';

	    $loop_subpag = new WP_Query($args);
	    if( $loop_subpag->have_posts() ):
	    while( $loop_subpag->have_posts() ): $loop_subpag->the_post();

	    	$childpages .= '<li>' . get_the_title() . '</li>';

	    endwhile;
	    endif;
	    $childpages .= '</ul>';
	    wp_reset_postdata();

		return $childpages;

	}

	add_shortcode( 'childpages', 'childpages_shortcode' ); ?>

How could this be edited so that in the shortcode, you can specify to only show pages that have a title that starts with an "A", "B", or "C"? Is this possible?

Hi can use conditionals inside the loop with the substr function http://php.net/manual/en/function.substr.php