There is a  record for Mary Langdon, Christened December 3, 1727 in Portsmouth, New Hampshire. Unfortunately, there is no notation of her parents.

I discovered documentation of a mourning ring for Mary Langdon on the website of the New Hampshire Historical Society. It is made of gold and has a rectangular faceted crystal over a paper skull with foil mat in a raised fluted setting flanked by two square crystals. The markings read “M. LANGDON:OB:28 OCT: 1736.AE8.” According to the Society, she was thought to be the daughter of Mark and Mehitable Langdon. To see a picture of the ring and more information, follow this link to the Society’s webpage.  Ring

In May of 1735, a disease called “throat distemper” of the most malignant kind, broke out in Kingston, New Hampshire. Its symptoms were a swelled throat, with white or ash-colored specks, an efflorescence on the skin, great debility of the whole system, and a tendency to putridity. It was the most fatal that the country had ever known. It particularly affected children.
It continued to spread throughout New Hampshire into the next year, and very few children escaped. This may have been the cause of Mary’s death.

A brief history of epidemic and pestilential diseases  page 223

There is no stone, nor a record of a Mary Langdon being buried in the Point of Graves. When I am walking the west end of the cemetery, I feel the presence of a little girl… the apple of her Daddy’s eye. Whether this is Mary, I do not know, but I light a candle for her memory.

Mary Langdon
born circa December 1727
died October 28, 1736
8 years old