Your great-great-grandfather, John, married your great-great-grandmother, Mary. You have found the marriage date – 1856. In the 1860 census, you find that they not only have children whose last name is Smith (John and Mary’s last name), but also children (listed as sons and daughters) who have the last name of Jones. Who are these children? Orphans? Step-children of John’s?
It is important to investigate these children. It could be that they are children of a relative you died. It could be that they are children of Mary Smith and her first husband (Samuel Jones).
Do not assume that these children are orphans. They may be family!