According to Paste Magazine:
Bernie Sanders, Hillary Clinton’s biggest challenger in the Democratic presidential primary, has one son. His name is Levi, and he has three adopted grandchildren from China. When Sanders married his second wife, Jane, she had three children of their own, and those children now have four children of their own. Sanders considers all seven his grandchildren, as anyone would, even though he’s not related to them by blood.
Clinton, conversely, has one daughter, Chelsea, and Chelsea has a baby daughter named Charlotte
I hope she just misspoke, otherwise it would be bizarre.