I raided my stash of solid-colored scrapbook paper. I simply traced a circular plate on the red sheet of paper and cut it out. If you are working with an older child, you can ask them to trace and cut, but I didn't want my son to get bored before the important stuff, so I did it quickly myself. The full circle represents the child, so my son labeled it 'Me' and '1.' Then, we worked on making three more circles, divided into halves, quarters, and eighths. The halves represented me and my husband (Mom & Dad), the quarters are his grandparents, and the eighths represent his great-grandparents. I had my son write the fractions on each piece, and I helped him label the grandparent ones. To keep it simple, I didn't put actual names on the great-grandparent pieces; I felt like that would be a bit confusing. I didn't want him getting lost in the names when I wanted the activity to have more of a math focus.
We treated it like a puzzle and put together the pieces for each 'generation' to make a whole circle. I explained to him that he is made up of parts of me, but also parts of Grandma and Grandpa because I am made of parts of them.
My 3.5 year old daughter was right there with us the whole time, so everything we talked about, she heard, too. It's tough to know how much she understood, but I let her 'do the puzzle' after her brother was done, and I tried my best walk her through both the fractions and the family relations. One variation you could do with this activity is to add photos of each person to each piece. I left those out for my son, because I actually wanted him to read the words AND focus on what the numerical fractions look like. For older kids, you could actually keep subdividing the pie pieces beyond just great-grandparents - that would be a GREAT way to help visualize the exponential increase of ancestors the further back in time you go.