Product Categs descendents of a specific parent

// WP_Term_Query arguments
$args = array(
	'taxonomy'               => array( 'product_cat' ),
	'parent'                 => 21,
	'number'                 => 5,
	'offset'                 => 10,
	'order'                  => 'ASC',
	'orderby'                => 'name',
	'hide_empty'             => true,
);

// The Term Query
$term_query = new WP_Term_Query( $args );

// The Loop
if ( ! empty( $term_query ) && ! is_wp_error( $term_query ) ) {
	// do something
} else {
	// no terms found
}