first you can know the relationship between child post and parent post try to figure it out or just try this code
$query = new WP_Query( array(
'post_parent' => get_theID(),
'posts_per_page' => 3, //shows only 3 children. If you want to show all of them, comment this line
));
while($query->have_posts()) {
$query->the_post();
/*Output the child markup here*/
the_content(); //Outputs child's content as it is
}
wp_reset_query();
?>