如何实现当前页面有二级子栏目就自动显示，没有二级子栏目的时候显示为空，不要显示所有的顶级栏目，以下写法怎么修改？

{loop $related $c}

                        <li>

                            <p> {$c.name} </p> 

                            <div class="three">

                                {if $c.child}

                                {category pid=$c.id return=cx}

                                <a href="{$cx.url}">{$cx.name}</a>

                                {/category}

                                {else}{/if}

                            </div>

                        </li>

 {/loop}