Brian has just rained on my parade as I was about to say the same thing. I have several cases of grandchildren living with grandparents in censuses and every one I have been able to confirm has been the child of an unmarried daughter.
It was much easier for a young unmarried woman to find a husband without a baby in tow and so the child often stayed with grandparents while the mother appeared childless and single. If the child does not appear in the subsequent censuses, it may be as simple as the child dying young. However, they may have been reunited with Mum after her marriage and then taking the step-father's name. Or maybe the child is with the real father who has belatedly accepted responsibility. Some creative searching is called for. Look in the next census for a child in his teens who is with a family now, but wasn't in the earlier censuses. If after 1837, get the birth certificate, which may make mention of the father. Look under his name. Search the child's first name and place of birth only - this may bring up a corrupted spelling of the real name or a different surname which may be the one you want. Look for marriages of daughters - their censuses may contain a child born before the marriage. To answer your specific case, if John and Mary Smith have a grandson Jim, I give them a child Smith, no first name, and add Jim to him. Good luck. Tony Legacy User Group guidelines: http://www.LegacyFamilyTree.com/Etiquette.asp Archived messages after Nov. 21 2009: http://www.mail-archive.com/legacyusergroup@legacyusers.com/ Archived messages from old mail server - before Nov. 21 2009: http://www.mail-archive.com/legacyusergroup@legacyfamilytree.com/ Online technical support: http://www.LegacyFamilyTree.com/Help.asp Follow Legacy on Facebook (http://www.facebook.com/LegacyFamilyTree) and on our blog (http://news.LegacyFamilyTree.com). To unsubscribe: http://www.LegacyFamilyTree.com/LegacyLists.asp