Return the number of kids for the room reserved and checked in by DAMIEN TRACHSEL on  Sep 21, 2010.
return rooms ;return #1 reserved by DAMIEN TRACHSEL ;return #2 on Sep 21 ,  2010 ;return #1 checked in by DAMIEN TRACHSEL ;return #4 on Sep 21 ,  2010 ;return #1 in both #3 and #5 ;return kids in #6 ;return number of  #7
['select', 'filter', 'filter', 'filter', 'filter', 'intersection', 'project', 'aggregate']