Peter and Mary were the third and fourth children of Pierre and Mary Justine Klein. Little is known of the two children. The only mention of them in Henry's letters was that they died of "bad water".
Peter died August 27, 1892 at the age of 4 years; Mary died on August 30, 1892 at the age of 10 years. They are buried in unmarked graves in the graveyard behind St. Aloysius Church in Greenbush, KS.
During one of my trips to Kansas, I did search for their graves. A monument has been erected memorializing those who did not have tombstones at the cemetery. Photos of the front and back of memorial are shown below.
Dr. Ash, a doctor in Erie tended to the children while they were ill. Pierre paid the $25 doctor bill with a clock that he and Justine had brought from France. The clock was wrapped in petticoats to help ensure it would survive the trip. Several years after the doctor died, Henry Klein redeemed the clock from the doctor's daughter. The clock is now in the possession of Finis Bryan. (See picture of clock below).
Front of Memorial
Peter and Mary's Memorial
Finis Bryan with clock that Pierre and Justine brought from France. It was wrapped in petticoats for the trip.
Front of Memorial 
Finis Bryan with clock that