code: function getDirChildren(parentId, items){
      var children = {};
      for(var id in items){
          if(items[id].ancestors[ items[id].ancestors.length-1 ] === parentId)
              children[id] = items[id];
      }
      return children;
  }
docs: helper - get only direct children of directory
  @param {String} parentId directory id
  @param {Object} items files
  @returns {Object}  children