I found a solution.
<?php
$term = get_queried_object();
$children = get_terms( $term->taxonomy, array(
'parent' => $term->term_id,
'hide_empty' => false
) );
if ( $children ) {
foreach( $children as $subcat ) {
$size = "thumbnail";
echo ' <div class=" cat-box ">';
$image = get_field('image', 'category_' . $subcat->term_id);
echo '<img src="' . $image . '" />';
echo '<a href="' . esc_url(get_term_link($subcat, $subcat->taxonomy)) . '">' . '<span> مقالات دسته</span>' . $subcat->name . ' </a>' . '</div>';
'</div>';
}
}
?>