Heide,
Actually DNA did not prove that Sally Hemmings children are those of Thomas Jefferson, nor can it (Y-DNA testing cannot prove this). All the DNA testing was able to prove was that at least one of Sally Hemmings' children was fathered by a male Jefferson who shared Y-DNA with Thomas Jefferson (who may have been Thomas himself). In fact, Thomas Jefferson's Y-DNA was not directly tested. Descendants of Thomas Jefferson's Uncle were tested to derive Y-DNA "sameness" of Thomas. We actually have no way of even knowing if Thomas Jefferson shared Y-DNA with his Uncle. He would, if they shared common paternal parentage, but that "fact" was only presumed in the study. Thomas Jefferson was not dug up to verify, and Thomas' wife did not bare any male children who survived.
Only by examining additional evidence, combined with the DNA evidence, could one conclude (and still not absolutely) that Thomas was the father.
To hear (and view) an excellent explanation on this specific topic (Jefferson and Hemmings) I strongly recommend watching the RootsTelevision presentation of a lecture by Dr. Eugene Foster, former University of Virginia Professor of Pathology. The lecture is almost 30 minutes in length, but I consider it essential viewing for learning what Y-DNA testing can and cannot do. The following link will take you to the video (hosted on Brightcove.com)
http://link.brightcove.com/services/link/bcpid463882991/bclid464024961/bctid236034471
For the record, I have been Y-DNA tested and have discovered and corresponded with another male Taber who shares my Y-DNA (with minor mutations). The paper record connects us as 8th cousins, twice removed.
Best Regards,
William Taber, Indianapolis