Change the WordPress Template for page.php if it has children

wp-page-has-children-conditional.php

<?php get_header(); ?>
<?php
	if (have_posts()) : while (have_posts()) : the_post();
	$pid = get_the_ID();
	$args = array(
		'post_parent' => $pid,
		'post_type'   => 'page', // Change as per post type
		'numberposts' => -1,
		'post_status' => 'publish' 
	); 
	$childp = get_children( $args );
	$numposts = count ( $childp );
	if( $numposts == 0 ) {
		get_template_part( 'page-single' ); // Template part if no children
	}
	else {
		get_template_part( 'page-parent' ); // Template part if has children
	} 
	endwhile; endif;
?>
<?php get_footer(); ?>