Loop through child images of a parent for a Nivo Slider

To get attached (i.e. child) images of a post, try using get_children(). e.g.:

<?php
$child_image_args = array(
    'post_mime_type' => 'image',
    'post_parent' => $postID,
    'post_type' => 'attachment'
);

$child_images = get_children( $child_image_args );
?>

Which returns an associative array of child images. Then, just loop through them, e.g. using wp_get_attachment_image(), to output. e.g.:

<div id="nivoslider">
    <?php
    foreach ( $child_images as $child_image ) {
        wp_get_attachment_image( $child_image->ID );
    }
    ?>
</div>

Nivo Slider integration is mostly out of scope for WPSE, but if you want to advance manually, change the manualAdvance setting to manual in your #nivoslider jQuery instantiation.