Isaac Newton never married and had no known children; some speculate that he was uninterested in romantic relationships, and there is no evidence to support the idea that he was ever romantically involved in any way with another person. Newton was very focused on scientific and mathematical matters and is said to have been apathetic to other subjects, even to the exclusion of romantic relationships.
Sir Isaac Newton had a difficult childhood and was known to experience bouts of emotional disturbance thought his life. This didn't keep him from making major steps in the fields of math and science, but he was apparently very puritanical when it came to sexual matters. According to Washington University's physics department, Newton ended a friendship over a lewd joke about a nun. In fact, it is widely believed that Newton died a virgin. Whether this is true or not, Newton acknowledged no children during his lifetime and there seems to be no evidence to even speculate that he had sexual relationships with women that could lead to the birth of a child.
Newton's legacy is one of intellectual pursuit and accomplishment, and all evidence suggests that his personal life was rarely, if ever, a source of joy or comfort for him.