Hi, I got the solution after going through other topics in this forum. Following is the working code. hope it will help others who might face the same problem.
$taxonomy_name = 'post_tag';
$term_id = get_queried_object_id();
$tax_images = get_option( 'taxonomy_image_plugin' );
$termchildren = get_terms( $taxonomy_name, array( 'parent' => $term_id, 'hide_empty' => true ) );
foreach ( $termchildren as $child ) {
$tax_imageid = $tax_images[$child->term_id];
$child_image = wp_get_attachment_image ($tax_imageid, 'thumbnail');
$string .= '<span class="tagbox"><a class="taglink" href="' . esc_url( get_term_link( $child, $child->taxonomy ) ) . '"><span class="tagname">'.$child_image.'<p>'.$child->name.'</p></span></a><span class="tagcount">'. $child->count .'</span></span>';
}
return $string;