您可以使用get_term_children() 获取术语的子项，但它只返回ID，因此您可以使用get_term_by() 将其转换为id

方法3

此方法基于WP内置的get\\u term\\u children（）和\\u get\\u term\\u hierarchy（），但已转换为支持slug。这里提供了整套函数供参考。

类似内置版本，返回unlimited number of children

// this is based on WP Core, return the immediate 1 level of children
function get_term_children_in_slug( $term_slug, $taxonomy ) {
    if ( ! taxonomy_exists( $taxonomy ) ) {
        return new WP_Error( \'invalid_taxonomy\', __( \'Invalid taxonomy.\' ) );
    }

    $term_data = _get_term_hierarchy_in_slug( $taxonomy );
    $terms = $term_data[\'children\'];
    $term_slug_ids = $term_data[\'term_slug_ids\'];

    if ( ! isset( $term_slug_ids[ $term_slug ] ) ) {
        return array();
    }

    if( ! isset( $terms[ $term_slug_ids[ $term_slug ] ] ) ) {
        return array();
    }

    $children = $terms[ $term_slug_ids[ $term_slug ] ];

    // find children of children
    foreach ( (array) $terms[ $term_slug_ids[ $term_slug ] ] as $child_slug => $child_id ) {
        if ( $term_slug === $child_slug ) {
            continue;
        }

        if ( isset( $terms[ $term_slug_ids[ $child_slug ] ]) ) {
            $children = array_merge( $children, get_term_children_in_slug( $child_slug, $taxonomy ) );
        }
    }

    return $children;
}

// this is based on WP Core for get_term_children() but support slug instead
function _get_term_hierarchy_in_slug( $taxonomy ) {
    if ( ! is_taxonomy_hierarchical( $taxonomy ) ) {
        return array();
    }

    // WP Builtin with cache by saving to option, reduce performance hit
    $children = get_option( "{$taxonomy}_children_slug" );

    if ( is_array( $children ) ) {
        return $children;
    }

    $children = array();
    $terms = get_terms( \'category\', array(
        \'hide_empty\' => false,
        // \'orderby\'                => \'id\', // haven\'t used in test, optional
        \'fields\'                 => \'all_with_object_id\',
    ) );

    $term_ids = []; // as cache to find out terms parent slug
    $compare = [];

    // all parents become level 1 id => level 2 id structure
    foreach ( $terms as $key => $term ) {
        $term_ids[ $term->slug ] = $term->term_id;
        if ( $term->parent > 0 ) {
            // $compare[ $term->slug ][] = $term->parent;
            $children[ $term->parent ][$term->slug] = $term->term_id;
        } 
    }

    update_option( "{$taxonomy}_children_slug", $children );

    // children for use, term ids for matching
    return array(
        \'children\' => $children,
        \'term_slug_ids\' => $term_ids
    );
}

// add clean up cache logic together with builtin clean up
add_action( \'clean_taxonomy_cache\', \'custom_clean_up_term_cache\' );
function custom_clean_up_term_cache( $taxonomy ) {
    delete_option( "{$taxonomy}_children_slug" );
}

方法2（推荐的方法，因为它是最简单的方法）Asker将第一个答案中的get\\u term\\u by（）与get\\u categories（）结合使用此方法

取决于args，可以返回直系后代或包括grandchilren在内的所有子代引用posts

// this method only return 1 level of immediate children
function get_term_children_in_slug_approach2( $term_slug ) {
    $parent = get_term_by( \'slug\', $term_slug, \'category\' );
    $term_slugs = (get_categories([
        \'taxonomy\' => \'category\',
        \'parent\' => $parent->term_id,
        \'hide_empty\' => false, // in the test, have no posts
    ]));

    return $term_slugs;
}

// the following return children and grandchildren
function get_term_children_in_slug_approach2( $term_slug ) {
    $parent = get_term_by( \'slug\', $term_slug, \'category\' );
    $term_slugs = (get_categories([
        \'taxonomy\' => \'category\',
        \'child_of\' => $parent->term_id,
        \'hide_empty\' => false, // in the test, have no posts
    ]));

    return $term_slugs;
}

方法1因为WP内置工具是基于ID的，所以使用内置get\\u term\\u chilren（）并不简单，需要进行ID-to-slug搜索。

返回the first immediate level of children

function getChild ( $slug ) {
    $term = get_term_by( \'slug\', $slug, \'category\' );
    $term_children = get_term_children( $term->term_id, \'category\' );

    // return a list of children id
    if( $term_children ) {
        return get_term_children( $term->term_id, \'category\' );
    }

    return $term_children;
}

获得子id列表后，可以将其转换回slug

// helper for retrieve slug from $term ID
function get_term_slug( $id ) {
    $term = get_term_by( \'id\', $id, \'category\' );
    // var_dump($term);
    if( $term ) {
        return $term->slug;
    }

    return $term;
}

// get a list of terms slug from term id
$term_slugs = [];
$term_children_ids = getChild( \'level1\' ); // example

foreach ($term_children_ids as $key => $term_id) {
    $term_slugs[] = get_term_slug( $term_id );
}