[WordPress] Determine if a given taxonomy term has children or does not have children.

1-check-if-term-has-children.php

<?php
// First, read the reads
$materials = wp_get_post_terms( get_the_ID(), 'acme_materials' );

foreach ( $materials as $material ) {

  if ( count( get_term_children( $material->term_id, 'acme_materials' ) ) > 0 ) {
    // The term has children
  }
  
}

2-check-if-term-has-no-children.php

<?php
// First, read the reads
$materials = wp_get_post_terms( get_the_ID(), 'acme_materials' );

foreach ( $materials as $material ) {

  if ( count( get_term_children( $material->term_id, 'acme_materials' ) ) === 0 ) {
    // The term has no children
  }
  
}

Small typo: In the first example, // The term has no children should be // The term has children :)

Besides that, I'd probably just use if ( get_term_children( ... ) ) since this boolean check equals false for an empty array. No need to use count().