Customizing children comments in wp_list_comments in wordpress

What I want is like this: Click to see the picture
But,at last It came up with like this:
Click to see the picture
(I can’t put img, so I put the picture to my blog!)
Here Is Code In My comment.php Where Show The Comments:

<?php wp_list_comments('type=comment&callback=comment_activity_list');?>

and this is the code of function “comment_activity_list” in my function.php:

<?php if (!function_exists("comment_activity_list")){
		function comment_activity_list($comment, $args, $depth){
		$GLOBALS['comment'] = $comment;
?>
			<ol class="clist">
					<li id="discussion-<?php comment_ID() ?>" class="discussion">
						<div class="discussion-post clearfix">
							<div class="gravatar"><?php echo get_avatar( $comment, 45); ?></div>
							<div class="block">
								<a class="discussion-username"><?php echo get_comment_author_link() ?></a>
								<div class="discussion-text">
							    	<?php comment_text()?>
									<?php if ($comment->comment_approved == '0') : ?>
							        	<p><em><?php _e('Your comment is awaiting moderation.'); ?></em></p>
							        <?php endif; ?>
						    	</div>
								<!--.discussion-text-->
		            <div class="discussion-meta">
		            	 <?php delete_comment_link($comment->comment_ID,'class="btn red"')?>- <?php comment_reply_link(array_merge( $args, array('depth' => $depth, 'max_depth' => $args['max_depth']))) ?> - <?php if(!function_exists('how_long_ago')){comment_date('M d, Y'); } else { echo how_long_ago(get_comment_time('U')); } ?>
		            </div>
		            <!--.discussion-meta-->
							</div>
							<!-- .discussion-post -->
						</div>
						<!-- .discussion-post -->
        	</li>
        </ol>
<?php
		}
	}?>

How can I Customize the children comments ? Any one can hepl me?
Thx In Advance!