code: function _readChild(stat, dirpath, name, callback) {
    _read(stat, path.join(dirpath, name), callback);
  }
docs: Ensures the child of the parent directory may provide its data.
  @param {Function} stat - Function of fs module fs.stat or fs.lstat.
  @param {String} dirpath - Path of the parent directory on file system.
  @param {String} name - File name of the child.
  @param {Function} callback - Callback that expects a possible error
  and child data.