jQuery(document).ready(function($) { // Usando el "no-conflict wrapper"
  $('#tab-description .item .children').each(function() {
    var $children = $(this).children('.child'); // Usando .children() y el alias $
    if ($children.length > 1) {
      $children.not(':last-child').css('border-bottom', '1px solid #ddd');
    }
  });
});