The question? How did Cass have a child?
Now, most of you have a fast quick answer; he had... private time... with his wife, and gave birth.
First, let me tell you things about Cassidy and Cass...
Cassidy:
Was around 60 years old when he travelled with the Chosen One. (2241)
Had a daughter named Cass.
Cass:
20-25 when travelling with the Courier. (2281)
Daughter of Cassidy
Mother was a tribal
So me and a friend of mine were discussing game history when it occured to me that Cassidy, who had a daughter, could not have POSSIBLY concieved Cass. If Cass is 20-25, this would place her birthdate around 2257-2263.
Seeing that Cassidy was more or less 60 in 2241, in 2261 Cassidy would be 80 years old. EIGHTY... That's well above and beyond the age where his seed will actually be viable to give offspring.
Buuuut he could have had her in 2241! No, because that'd make Cass 40-45 by the events of New Vegas, which would make her one very, very, very hot milf.
So my question to you is... How the hell could Cassidy have had a daughter that was actually his?