Display child pages in sidebar of parent page in wordpress

If you don’t want a list of Pages, then why are you calling wp_list_pages() in your code? that function returns a list of Pages.

You probably need to use get_posts() instead, and then loop through the results to output whatever $post content you want to display.

e.g. you could do something like the following:

<?php
global $post;
$child_pages = get_posts( array(
    'post_parent' => $post->ID
) );
?>
<ul>
<?php
foreach ( $child_pages as $child ) {
    ?>
    <li>
        <h3><?php echo $child->post_title; ?></h3>
        <div><?php echo $child->post_content; ?></div>
    </li>
    <?php
}
?>
</ul>

EDIT

If you need to access $post->ID from outside the Loop, do something like this inside the Loop:

$current_post_id = $post->post_ID;

Then, just use $current_post_id outside the Loop. (Note that you’ll only want to do this on template pages that display single Posts; otherwise, the value of $current_post_id will change on every cycle of the foreach loop.)

You could then change your get_posts() call accordingly:

$child_pages = get_posts( array(
    'post_parent' => $current_post_id
) );