JSFiddle - React, Tailwind, and code Playground

HTML

<div id="firstChild">
  <div id="second">x
     <div id="div_1">a</div>
  </div>
  <div id="third">y
     <div id="div_2">b</div>
  </div>
  <div id="fourth">z
     <div id="div_3">c</div>
  </div>
</div>

CSS

.test { background: #f00; }

JavaScript

$('#firstChild').find('[id^="div_"]').addClass('test');