ROCKVILLE, Ind., May 23 The Parke County grand jury was in recess today after a two day invetigation of possible negligence in a life in which six retarded children died. Prosecutor Earl Dowd said the grand jury will resume de liberations May 31 and will then make any report or return any indictments deemed valid. Dowd said 16 witnesses testi fied before the session ended late Wednesday. He said the grand jurors decided they want ed time to consider the case and might hear additional evidence later. The witnesses included Mr. and Mrs. William Johnson, the operators of the private home in which the children died. He said both waived immunity. Five children were killed out right and a sixth suffered fatal burns in a fire that swept the Johnson home May 3. Five other children were injured. Sheriff Charles A. Cooper said two teen-aged babysitters were caring for the children at the time of the fire. The Johnsons had left for a nearby veterans’ club. The state fire marshal’s office said in a report on the eve of the investigation that kerosene cans had been left next to a faulty electric dryer which ignit ed the blaze. It said also that the babysitters failed to summon firemen immediately. Witnesses at the investigation included Sheriff Cooper; Bernard Sweeney, investigator for the State fire marshal; Rock ville Fire Chief Bernard Lee, welfare officials and two pass ersbys who helped carry out the children. Albert Kelly, state welfare di rector, said Mrs. Johnson noti fied him that she is caring for four survivors in a home in near by Clinton. The fifth is still in a hospital.