Template:Descendants/child

Process one child for Descendants, as follows:
 * 1) add child to Property:desc1
 * 2) for each entry in Property:desc1 of child, add it to Property:desc2: child's children are our grandchildren
 * 3) for each entry in Property:desc2 of child, add it to Property:desc3: child's grandchildren are our great-grandchildren