Andy has had children several times over the centuries. The first few times it was because she was desperately hoping that they'd end up being like her, so she could stop being alone. Then, during less cynical times, after meeting Quynh and before losing her, it was because she liked adding life to the world sometimes, rather than just taking them. She never paid too much attention to what happened to any of them, beyond making sure they went to someone decent to be raised, but then Kozak's testing reveals that while none of Andy's kids ever ended up immortal, some of those children's descendants did.

Bonus: Further research reveals that Joe and Nicky are descended from the same ancestor and it's a close enough relationship that it gives them pause for exactly zero seconds but Booker absolutely teases them for it.