Add Class to Divs in an order of another

Add Class to Divs in an order of another

I have 2 parent Divs containing same number of children like below;
<div class="parent_1">
<div class="dir one">...</div>
<div class="dir two">...</div>
<div class="dir three">...</div>
....
</div>
<div class="parent_2">
<div class="dir">...</div>
<div class="dir">...</div>
<div class="dir">...</div>
...
</div>
I need to add the support classes of the parent_1 children's (.one, .two,
.three) to the parent_2's children in the same order.
Number of children will be created dynamically and both parents will have
the same number.