select all child div's in all parents div's

select all child div's in all parents div's

This is my code: I want to select all children classes
attribute(tbox,tarea,cts,tox) inside of all parent
var s = $('div.cts').children().attr('class');
alert(s);
but it showing only first parent first child class attribute
<fieldset id="tt">
<div class="cts">
<div class="tbox">
<input type="text"/>
</div>
</div>
<div class="cts">
<div class="tarea">
<input type="hidden">
</div>
</div>
<div class="cts">
<div class="tss">
<input type="password">
</div>
</div>
<div class="cts">
<div class="tox">
<input type="text">
</div>
</div>