A family tree usually shows your ancestors, not your descendants. The names of your parents should be in the spaces for the man and woman on the afghan, and the names of their parents and grandparents would be in the branches above.
I'm not really sure how it could work to use the names of their children, grandchildren, and great-grandchildren, although that is a very nice sentiment.
This site explains it a bit better than I do.
Pedigree, Direct Lineage or Ascendant Family Tree Chart
The Pedigree Family Tree Chart is sometimes called a Direct Lineage or Ascendant Family Tree. This is perhaps the most common type of family tree and the one most people think of when referring to family trees. The pedigree family tree begins with you (or a parent, or grandparent) and then follows a single bloodline or family name back through the generations as far back as you can go.
Descendant Family Tree Chart
A Descendant Family Tree Chart is the opposite of the Pedigree Family Tree Chart. This type of family tree chart starts with an ancestral couple pretty far back in the family history and then lists the descendants of that ancestral couple generation by generation until the present.
Maybe you could find an afghan with a Descendant family tree?
Something like this:
Ideally, the names of your parents should be at the top, with the children on the next level down, then the grands, then the great-grands.
If you really like the afghan you posted, I suppose you could put the names of the descendants in the branches, but there doesn't seem to be enough room for them all. Can you put more than one name on a branch?
Good luck, and congratulations to your parents!
