Sarah and her son were killed by a group of native Americans who advanced into Hatfield. This was in retaliation of what the colonists from that town did a year and a half ago when a group of these colonists invaded an Indian village made up of eastern Algonkian Indians, killing anyone who tried to escape.
From the Geni web site titled, "Raid on Hatfield (1677)":
At eleven o’clock on the bright fall morning of September 19, 1677, a group of about fifty natives attacked the north end of the frontier town of Hatfield, Massachusetts. Even though the colonists had built a defensive stockade the year before, they were caught off guard. The men were helping to frame a new house or working in the fields south of the palisade. The natives never even tried to enter the stockade, instead attacking the houses outside the twelve-foot walls. Some men standing on top of the new house were shot and fell; others were captured and bound. Thirteen homes were invaded; seven were burned. Women and children were killed or captured. The men in the fields saw the smoke and rushed back to the village, but by the time they got there, the Indians had marched their seventeen captives across the fields and turned north on the Poctumtuck path toward Deerfield. They were bound for Canada.
(1) She is married to Nathaniel Gunn.
They got married on November 17, 1658 at Springfield (Hampden County), Massachusetts Bay, British America, she was 18 years old.Source 1
(2) She is married to Samuel Kellogg.
They got married on November 24, 1664 at Hatfield, Massachusetts Bay, British America, she was 24 years old.Source 1