<div class="parent">
<div class="child1"></div>
<div class="child2"></div>
</div>
<div class="parent">
<div class="child1"></div>
<div class="child2"></div>
</div>
<div class="parent">
<div class="child1"></div>
<div class="child2"></div>
</div>
<div class="parent">
<div class="child1"></div>
<div class="child2"></div>
</div>
交换child1和child2的顺序的正确解决方案是什么?