Children of Isaac Newton and Sarah Belknap: Margaret, b. 30 Aug 1729. "She is not mentioned in her father's will, and probably died young. Her birth is recorded as "dau. of Isaac Jr. and Sarah", but there was no other Isaac and Sarah Newton whose daughter she could be except this couple."
[Note: The son Isaac Jr. b. 1723, did marry 1750 a wife Sarah, but they could not be her parents unless the date is wrong by more than two decades, e.g., 1759 or a similar type of error.]