Team Drive列出所有文件夹，包括儿童

I can get access to the upper level (root level) folders for my TeamDrive, but have bee unsuccessful find out how to get all the sub-folders (the children). What I'd like to perform is getting all children with one call...

I've seen the teamdrive REST API here https://developers.google.com/drive/api/v3/reference/teamdrives/list but this only retrieves the root level.

I can retrieve the next level down by taking the $folderId (this is the folder ID that we're trying to get the children for) and performing 2 calls to retrieve the next level

        $optParams = array(
            'supportsTeamDrives' => true,
        );
        $results = $service->files->get($folderId, $optParams);
        $teamDriveId = $results["teamDriveId"];

then using the resulting $teamDriveId and calling a files->listFiles

        $optParams = array(
        'q'                     => "'{$folderId}' in parents and trashed = false and mimeType = 'application/vnd.google-apps.folder'",
        'pageSize'              => $pageSize,
        'corpora'               => 'teamDrive',
        'includeTeamDriveItems' => true,
        'supportsTeamDrives'    => true,
        'teamDriveId'           => $teamDriveId,    // this must be the parent Id
        'orderBy'               => 'name',
        'pageToken'             => $nextPageToken,
    );

    $results = $service->files->listFiles($optParams);
    $nextPageToken = !isset($results["nextPageToken"]) ? "" : $results["nextPageToken"];

This will be slow as the folders can expand for sometime... Does anyone know how to get the FULL folder & all the children structure for my Team Drives? Does anyone know if this is even allowed? I've tried a lot of different options in my PHP code and the various REST API function test areas.