The Worcester VR's found in NEHGS Database indicate the two births you reference and no others in Worcester. They were married in Newton, MA in 1741. The family seems to have moved to CT where another child of Nathaniel and Marther is found in Ashford, Windham County, CT. I checked the Ashford record and and confirmed this as Nathaniel son of Nathaniel and Marther b. Sept. 16., 1749. There is a family tree on ROOTSWEB.com that covers this family well. Although information must always be verified from this source there is an indication that the family removed to Stephentown, Rennselaer county, NY and also to Washington County, NY. It appears that although there are several nathaniel Spring's you have a Revolutionary soldier connection that may enable you to obtain a pension file if the correct Nathaniel is identified.